Illumination device and liquid crystal display device using the same

ABSTRACT

An illumination device is provided which can reduce a movement blur and a tailing phenomenon on a motion picture display while a drop in display brightness is suppressed, and which can suppress power consumption, can be made small and light, and can prolong the lifetime, and a liquid crystal display device using the same is provided. A light source control part of a control circuit synchronizes a latch pulse signal outputted from a gate driver control part to a gate driver, and outputs light emission control signals to respective light source power supply circuits. The respective light source power supply circuits change emission states of cold cathode fluorescent lamps to one of a first to a third emission states on the basis of the inputted light emission control signals, and illuminate an LCD panel from a rear surface of a display area. A first stage emission state is a non-lighting state, a second stage emission state is a maximum lighting state in which maximum lighting brightness is obtained, and a third emission state is an intermediate lighting state in which brightness of about one half of the second stage emission state is obtained.

This is a divisional of application Ser. No. 10/696,504, filed Oct. 29,2003.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an illumination device for illuminatinga display area of a liquid crystal display device, and a liquid crystaldisplay device using the same. Particularly, the invention relates to anillumination device which improves motion picture blur and a tailingphenomenon at the time of display of motion pictures, and a liquidcrystal display device using the same.

2. Description of the Related Art

[First Related Art]

As alternate means of a CRT (Cathode Ray Tube) which is a conventionaltypical display device, in recent years, an active matrix type liquidcrystal display device (hereinafter abbreviated to TFT-LCD) in which aTFT (Thin Film Transistor) or the like is provided as a switchingelement at each pixel has gone mainstream.

In principle, in the TFT-LCD, gradation data written into each pixel isheld for one frame period (equal to a period of a verticalsynchronization signal Vsync). In such a hold type display system, whena motion picture is displayed, the display can not respond to a quickimage change, and degradation in picture quality can occur in which animage blur and a tailing phenomenon are visually recognized.

In order to solve this problem, a method is proposed in which a displayperiod of gradation data of each pixel is limited to a specific periodin one frame period in synchronization with a vertical synchronizationsignal Vsync (for example, see undermentioned patent document 1).Besides, in order to realize the method, a method is proposed in whichan illumination area of an illumination device, such as a backlightunit, for illuminating an image display area of a TFT-LCD is dividedinto plural parts in the image display area, illumination of therespective divided areas is sequentially turned on and off, and adisplay period (illumination period) of each divided area is limited toa specific period in one frame period (for example, see patentundermentioned documents 2 to 5).

[Second Related Art]

More specifically, a cold cathode fluorescent lamp (CCFL) is used as alight source of a backlight unit for a conventional TFT-LCD, and adisplay area of the LCD is illuminated while the cold cathodefluorescent lamp is always turned on. When a motion picture display iscarried out while the cold cathode fluorescent lamp is always in alightening state, in the case where gradation data is rewritten in aframe period (period) of, for example, 16.7 ms and the motion picture isdisplayed, since a response time of a liquid crystal molecule to achange in electric field intensity is several tens ms, next gradationdata is written before the response of the liquid crystal molecule iscompleted, and accordingly, there occurs a disadvantage that a “blur” isseen to be produced on the motion picture display.

Besides, in the TFT-LCD, since data written in a certain frame is helduntil the gradation data is rewritten in the next frame, a display blurcalled trail vision on the basis of a human engineer viewpoint is alsovisually recognized, and therefore, there is a problem that the degreeof the blur of the motion picture becomes large.

The above problem is explained in detail in undermentioned nonpatentdocument 1 and nonpatent document 2. The nonpatent document 2 disclosesa study to improve the motion picture blur by turning on and off thecold cathode fluorescent lamp of the backlight unit.

However, when the cold cathode fluorescent lamp of the backlight unit issimply turned on and off, an afterimage of a former frame remains, andthis is visually recognized as a ghost of a moving body in an image.Especially in the case where a line segment is moved, a tailingphenomenon is visually recognized in which the line segment is seendoubly or triply, which causes the display quality to be remarkablydegraded.

Then, as a countermeasure against the ghost, a scan backlight system isproposed in which a backlight unit is divided into plural areas and alight source of each divided area is turned on and off insynchronization with the writing of gradation data. In order to realizethis, a direct type backlight unit is proposed in which plural lightsources such as fluorescent lamps are arranged substantially in parallelto a gate bus line (scanning line), and the light sources aresequentially turned on and off for a plurality of the respective pluraldivided areas.

FIG. 74 shows a section obtained by cutting a direct type backlightunit, which is used for a conventional TFT-LCD to support a motionpicture display, along a plane orthogonal to a tube axial direction of acold cathode fluorescent lamp, and a brightness distribution ofillumination light from the backlight unit. In FIG. 74, a gate bus line(not shown) of a TFT-LCD 1008 is extended in a direction vertical to apaper plane. Besides, a display start line of one frame exists at an“upper (top)” side of the left in the drawing, and a final display lineexists at a “lower (bottom)” side of the right in the drawing. Abacklight unit 1000 is divided into four areas from the “top” to the“bottom” of the drawing. The respective divided areas are separated byU-shaped lamp reflectors (reflection plate) 1002, and a cold cathodefluorescent lamp 1004 whose tube axis extends in the extending directionof the gate bus line is disposed in each of the lamp reflectors. A lightemission port of the backlight unit 1000 is disposed at the rear surfaceof a display area of the TFT-LCD 1008 through a transmission diffusedplate 1006.

[Third Related Art]

In recent years, the screen of the TFT-LCD 1008 has been enlarged andits brightness has been intensified, and also in the backlight unit1000, there occurs a necessity to improve light emission brightness byincreasing the number of luminous tubes.

Besides, as compared with a CRT, the TFT-LCD 1008 continues to outputlight for one frame, so that an image blur occurs in a motion picturedisplay, and picture quality performance is inferior to the CRT ofimpulse light emission (undermentioned nonpatent document 3). In orderto cope with this, the patent document 1 proposes a method of causing anLCD to perform an impulse operation, and a technique to realize animpulse operation is disclosed in undermentioned patent document 2 orpatent document 6 in which the backlight unit 1000 is duty (flicker)driven in a unit of one frame, and in undermentioned patent document 7in which image data and black writing are alternately performed.However, when the duty driving or black writing is merely performed, alight output time is reduced and the brightness of a display is lowered,and accordingly, it is necessary to raise the output of the backlightunit 1000 at the same time.

[Fourth Related Art]

Besides, in a scan type or a blinking type surface illumination deviceand liquid crystal display device, a cold cathode fluorescent lamp or anLED is used as a light source, and for the purpose of improving thequality of motion pictures (reducing the blur of a contour), dutydriving is performed in which turning on and off a light is repeated ata frequency of 60 Hz.

[Fifth Related Art]

FIG. 75 shows a structure of a direct type backlight unit used for aconventional TFT-LCD to support a motion picture display when viewedfrom a display area side. As shown in FIG. 75, a backlight unit 1000 isdivided into four areas from the top to the bottom of the drawing.Respective divided areas 1010 to 1013 are separated by lamp reflectors(reflection plates) 1002 (not shown in FIG. 75) having U-shapedsections. A cold cathode fluorescent lamp 1004 whose tube axis extendsin the extending direction of a gate bus line of a TFT-LCD 1008 (notshown in FIG. 75) is disposed in each of the lamp reflectors 1002. Alight emission port of the backlight unit 1000 is disposed at the rearsurface of a display area of the TFT-LCD 1008 through a transmissiondiffused plate 1006. As a scan type illumination device, this directtype is mainstream.

FIG. 76 shows a structure of a sidelight type backlight unit as anotherscan type illumination device. As shown in FIG. 76, respective dividedareas 1010 to 1013 of a backlight unit 1000 respectively include lightguide plates 1020 optically separated from each other and arranged in aplane. A dot-like light source such as an LED 1022 is disposed at eachof both end faces of each of the light guide plates 1020 to 1023.

Incidentally, the documents of the related art are as follows:

[Patent Document 1]

JP-A-9-325715

[Patent Document 2]

JP-A-11-202285

[Patent Document 3]

JP-A-11-202286

[Patent Document 4]

JP-A-2000-321551

[Patent Document 5]

JP-A-2001-125066

[Patent Document 6]

JP-A-5-303078

[Patent Document 7]

JP-A-2001-184034

[Patent Document 8]

JP-A-2000-194312

[Nonpatent Document 1]

Television Image Information Engineering Handbook, Ohmsha P70 to 71

[Nonpatent Document 2]

ASIA Display/IDW'01 P1779-1780, 1781-1782

[Nonpatent Document 3]

Yasuichiro Kurita, “Display System of Hold-Type Display and PictureQuality in Motion Picture Display”, Preprint of First LCD Forum

[Nonpatent Document 4]

J. Hirakata et al.: “High Quality TFT-LCD System for Moving Picture”,SID 2002 Digest, p. 1284-1287 (2002)

[Nonpatent Document 5]

D. Sasaki et al.: “Motion Picture Simulation for DesigningHigh-Picture-Quality Hold-Type Displays”, SID 2002 Digest, p. 926-929(2002)

[Nonpatent Document 6]

K. Sekiya et al.: “Eye-Trace Integration Effect on The Perception ofMoving Pictures and A New Possibility for Reducing Blur on Hold-TypeDisplays”, SID 2002 Digest, p. 930-933 (2002)

[Nonpatent Document 7]

H. Ohtsuki et al.: “18.1-inch XGA TFT-LCD with Wide Color Reproductionusing High Power LED-Backlighting”, SID 2002 Digest, p. 1154-1157 (2002)

[Nonpatent Document 8]

Gerald Harbers, and two others, “LED Backlighting for LCD-HDTV,[online], Internet <URL:http://www.lumileds.com/pdfs/techpaperspres/IDMC_Paper.pdf>

[Problem of First Related Art]

In the case of the first related art, when the illumination light sourceis simply turned on and off, the display brightness is remarkablylowered, and there arises a problem that the LCD has low brightness andlow picture quality. For example, in the case where the display area isdivided into five divided areas, and illumination of 20% is sequentiallyperformed in one frame, in the one frame period, the brightness becomes⅕ as compared with the time of illumination of 100%. On the other hand,when a lighting time in each divided area is made long, although thebrightness is raised, there arises a problem that degradation of picturequality such as motion blur becomes remarkable.

[Problem of Second Related Art]

In the direct type backlight unit 1000 of the second related artexplained by using FIG. 74, since the cold cathode fluorescent lamp 1004is disposed to be close to the rear surface of the TFT-LCD 1000, asshown in the upper stage of FIG. 74, there is a defect that unevenbrightness is apt to occur. The horizontal axis of the upper stage ofFIG. 74 indicates the position of the TFT-LCD 1008 on the rear surfaceof the display area, and the vertical axis indicates the brightness. Inthe direct type backlight unit 1000, as indicated by a brightnessdistribution curved line of the upper stage of FIG. 74, a difference inbrightness is apt to occur between a place just above the cold cathodefluorescent lamp 1004 and a boundary of the adjacent cold cathodefluorescent lamps 1004, and there is a defect that uneven brightness isapt to occur by this. As a method of causing the difference inbrightness to be inconspicuous, a method has been adopted in which a gapbetween the transmission diffused plate 1006 and the TFT-LCD 1008 iswidened to diffuse and mix the illumination light, or a method has beenadopted in which the degree of diffusion of the transmission diffusedplate 1006 is raised to further diffuse and uniform the light emitted toa space just above the cold cathode fluorescent lamp 1004. However, theformer has a problem that the thickness of the device is increased, andthe latter has a problem that the diffused light is again incident onthe cold cathode fluorescent lamp and is absorbed, and the lightquantity is lowered.

[Problem of Third Related Art]

When the light emission brightness of the cold cathode fluorescent lamp1004 of the backlight unit 1000 is raised to increase the brightness asin the third related art, there arises a problem that power consumptionand cost are increased. Further, even in the case where an image havinga low average brightness on a screen is displayed, the light emissionbrightness of the cold cathode fluorescent lamp 1004 remains high, andaccordingly, the temperature of the TFT-LCD 1008 rises. It is alsonecessary to improve the cooling structure for suppressing thistemperature rise, and according to circumstances, there arises a problemthat the device volume of the TFT-LCD 1008 is increased.

[Problem of Fourth Related Art]

In the cold cathode fluorescent lamp or the LED, since current fed tocause light emission or power supply is restricted, there is a problemthat the brightness can not be made high by the duty driving. That is,in order to increase the supplied current, a stabilizer of the coldcathode fluorescent lamp becomes large. Thus, the stabilizer becomesheavy and thick, and further its cost becomes high. Furthermore, thereis a problem that with the increase of the current, the driving voltagebecomes high, so that the current-to-light conversion efficiency of thecold cathode fluorescent lamp is lowered, and the lifetime becomesshort. Besides, for example, in a display device of a portableelectronic equipment such as a notebook computer, strict restrictionsare imposed on the power supply. Also in a solid emission type lightsource such as an LED, there arises a problem that the current-to-lightconversion efficiency is lowered by the current increase, and thelifetime becomes short.

[Problem of Fifth Related Art]

In the direct type backlight unit 1000 of the fifth related artdescribed by use of FIG. 5, since the cold cathode fluorescent lamp 1004is disposed to be close to the rear surface of the TFT-LCD 1008, thereis a defect that the brightness distribution is apt to become irregular,and the uneven brightness on the display is apt to occur.

Besides, in the sidelight type backlight unit 1000 of the fourth relatedart described by use of FIG. 76, since a light source, such as the coldcathode fluorescent lamp 1004, having a relatively large light emissionquantity and a long length can not be used, there is a problem that thebrightness is low.

SUMMARY OF THE INVENTION

An object of the invention is to provide an illumination device whichcan reduce a movement blur and a tailing phenomenon on a motion picturedisplay while a drop in display brightness is suppressed, and a liquidcrystal display device using the same.

Besides, another object of the invention is to provide an illuminationdevice which can suppress power consumption, can be made small andlight, and can prolong the lifetime, and a liquid crystal display deviceusing the same.

The above objects can be achieved by an illumination device forilluminating a display area of an active matrix type liquid crystaldisplay device, which is characterized by comprising at least one lightsource capable of changing light emission brightness, at least onelight-emitting area for emitting light from the light source, and alight source control system for switching between a maximum lightingstate in which the light-emitting area is made to emit light at aspecified maximum brightness and an intermediate lighting state in whichthe light-emitting area is made to emit light at a specifiedintermediate brightness lower than the maximum brightness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a rough structure of an illumination deviceaccording to a first embodiment of the invention and a liquid crystaldisplay device using the same;

FIG. 2 is a view showing output timings of gate pulses GP outputted torespective gate bus lines 6 from a gate driver 12 in synchronizationwith the input of a latch pulse signal LP, and light emissionbrightnesses B(25) to B(28) of respective light-emitting areas 25 to 28in the illumination device according to the first embodiment of theinvention and the liquid crystal display device using the same;

FIG. 3 is view showing, as subjective evaluations by plural observers,display quality when a motion picture is displayed on a display area ofa TFT-LCD 1 shown in FIG. 1 while an illumination period at a maximumlighting brightness and a level of an intermediate brightness arechanged in the illumination device according to the first embodiment ofthe invention and the liquid crystal display device using the same;

FIG. 4 is a view showing a rough structure of an illumination deviceaccording to a second embodiment of the invention and a liquid crystaldisplay device using the same;

FIGS. 5A and 5B are views showing the rough structure of theillumination device according to the second embodiment of the invention,in which FIG. 5A is a sectional view taken along line A-A of FIG. 4 andshows a section obtained by cutting the illumination device (sidelighttype backlight unit) 40, which is used for a TFT-LCD 1 to support amotion picture display according to this embodiment, along a planeorthogonal to a tube axial direction of a cold cathode fluorescent lamp,and FIG. 5B shows a brightness distribution of illumination light fromthe illumination device 40 at a rear surface side of a display area ofthe TFT-LCD 1;

FIGS. 6A and 6B are views showing a modified example of the illuminationdevice 40 according to the second embodiment of the invention and theTFT-LCD 1 using the same;

FIGS. 7A to 7C are views for explaining another modified example of theillumination device 40 according to the second embodiment of theinvention, in which FIG. 7A shows an illumination device 40 in a statewhere a double-sided reflection member 64 is disposed in a gap betweenlight guide plates 51 and 52, FIG. 7B is a view showing the double-sidedreflection member 64, and FIG. 7C is a view showing another double-sidedreflection member 64;

FIGS. 8A and 8B are views for explaining an expression 1 in the secondembodiment of the invention, in which FIG. 8A is an enlarged view ofFIG. 7C, and FIG. 8B is a view showing the course of light in an endface at the side of the light guide plate 52;

FIGS. 9A to 9C are views for explaining still another modified exampleof the illumination device according to the second embodiment of theinvention and the liquid crystal display device using the same, in whichFIG. 9A is a view showing a rough structure of an illumination device ofthis modified example and a liquid crystal display device using thesame, FIG. 9B is a sectional view taken along line A-A of FIG. 9A and isa view showing a section obtained by cutting the illumination device(sidelight type backlight unit) 40, which is used for a TFT-LCD 1 tosupport a motion picture display according to this embodiment, along aplane orthogonal to a tube axial direction of a cold cathode fluorescentlamp, and FIG. 9C is a view showing a brightness distribution ofillumination light from the illumination device 40 at the rear side of adisplay area of the TFT-LCD 1;

FIGS. 10A and 10B are views showing subjective evaluation as to whetheror not a difference in picture quality from the original image is feltin a case where in a third embodiment of the invention, a ratio (dutyratio) of a lighting time of a backlight unit in one frame period ischanged, and further, gradation data is processed and liquid crystaltransmissivity is adjusted;

FIG. 11 is a view showing a rough operation procedure of a display dataconversion circuit 20 of an illumination device according to the thirdembodiment of the invention and a liquid crystal display device usingthe same;

FIG. 12 is a flowchart showing calculation of lightness Y and aprocedure of histogram creation in the display data conversion circuit20 of the illumination device according to the third embodiment of theinvention and the liquid crystal display device using the same;

FIG. 13 is a flowchart showing a procedure of calculating the number Mof pixels occupied by an image in the case where the image exists inonly a part of one frame (screen) in the illumination device accordingto the third embodiment of the invention and the liquid crystal displaydevice using the same;

FIG. 14 is a flowchart showing a procedure of calculating thresholdlightness Yα in the illumination device according to the thirdembodiment of the invention and the liquid crystal display device usingthe same;

FIG. 15 is a view showing a duty ratio selection lookup table used forselection of a duty ratio of a light source in the illumination deviceaccording to the third embodiment of the invention and the liquidcrystal display device using the same;

FIG. 16 is a view showing a signal control value selection lookup tablefor determining a control value when processed gradation data isoutputted to plural data bus lines 8, which is made to correspond to thethreshold lightness Yα in the illumination device according to the thirdembodiment of the invention and the liquid crystal display device usingthe same;

FIG. 17 is a view showing an example of duty driving in the illuminationdevice according to the third embodiment of the invention and the liquidcrystal display device using the same;

FIG. 18 is a view showing an example in which a sidelight type backlightunit as the illumination device according to the third embodiment of theinvention is disposed in an LCD panel;

FIG. 19 is a view showing an example in which cold cathode fluorescentlamps A and B of the sidelight type backlight unit as the illuminationdevice according to the third embodiment of the invention are dutydriven;

FIG. 20 is a view showing, as the illumination device according to thethird embodiment of the invention, a scan type backlight unit in whichcold cathode fluorescent lamps A to F are disposed at the rear surfaceof a panel display surface;

FIG. 21 is a view showing an example in which the cold cathodefluorescent lamps A to F of the illumination device according to thethird embodiment of the invention are duty driven;

FIG. 22 is a view showing an example in which the sidelight typebacklight unit of the illumination device according to the thirdembodiment of the invention is disposed in an LCD panel;

FIG. 23 is a view showing an example in which the cold cathodefluorescent lamps A to D of the sidelight type backlight unit of theillumination device according to the third embodiment of the inventionare duty driven;

FIG. 24 is a view showing an example in which a direct type backlightunit of the illumination device according to the third embodiment of theinvention is disposed in an LCD panel;

FIG. 25 is a view showing an example in which cold cathode fluorescentlamps A to H of the direct type backlight unit of the illuminationdevice according to the third embodiment of the invention are dutydriven;

FIG. 26 is a view showing an example in which the direct type backlightunit of the illumination device according to the third embodiment of theinvention is disposed in an LCD panel;

FIG. 27 is a view showing an example in which LEDs A to T of the directtype backlight unit of the illumination device according to the thirdembodiment of the invention are duty driven;

FIG. 28 is a view showing a state in which in a display device providedwith a scan type backlight unit shown in FIG. 1, a duty ratio is 80%,the first 20% of one frame period is turned off, and the remaining 80%of the period is totally turned on;

FIG. 29 is a view showing a duty driving method for solving a problem ofthe backlight of FIG. 28 by using the illumination device according tothe third embodiment of the invention;

FIG. 30 is a view showing a backlight structure according to example 1of a fourth embodiment of the invention;

FIG. 31 is a view showing driving waveforms of a backlight according tothe example 1 of the fourth embodiment of the invention;

FIG. 32 is a view showing a backlight structure according to example 2of the fourth embodiment of the invention;

FIG. 33 is a view showing driving waveforms of a backlight according tothe example 2 of the fourth embodiment of the invention;

FIG. 34 is a view showing a specific timing chart of the backlightaccording to the example 2 of the fourth embodiment of the invention;

FIG. 35 is a view showing a specific timing chart of the backlightaccording to the example 2 of the fourth embodiment of the invention;

FIG. 36 is a view showing a specific timing chart of the backlightaccording to the example 2 of the fourth embodiment of the invention;

FIG. 37 is a view showing a specific timing chart of a backlightaccording to example 3 of the fourth embodiment of the invention;

FIG. 38 is a view showing a specific timing chart of the backlightaccording to the example 3 of the fourth embodiment of the invention;

FIG. 39 is view showing, as subjective evaluations by plural observers,display quality when motion pictures are displayed on a display area ofa TFT-LCD 1, while a current value (relative value) in a maximumlighting state S2 is made 10 and intermediate lighting states S3 and S4of FIG. 38 are changed in the backlight according to the example 3 ofthe fourth embodiment of the invention;

FIG. 40 is a view showing characteristics of a cold cathode fluorescentlamp;

FIGS. 41A and 41B are views showing an effect obtained when anillumination device according to the fourth embodiment of the inventionand its duty driving method are used;

FIGS. 42A and 42B are views showing an effect obtained when theillumination device according to the fourth embodiment of the inventionand its duty driving method are used;

FIGS. 43A and 43B are views for explaining example 4 of the illuminationdevice according to the fourth embodiment of the invention;

FIG. 44 is a view showing a result obtained when the duty driving shownin FIG. 37 or 38 is performed for a backlight unit 75 of the example 4of the illumination device according to the fourth embodiment of theinvention;

FIGS. 45A and 45B are views showing a conventional direct type backlightstructure and duty driving as a comparative example of the illuminationdevice according to the fourth embodiment of the invention;

FIG. 46 is a view showing the duty driving of the conventional directtype backlight unit as the comparative example of the illuminationdevice according to the fourth embodiment of the invention;

FIG. 47 is a view showing a backlight unit 75′ according to example 5 ofthe illumination device of the fourth embodiment of the invention;

FIG. 48 is a view showing a backlight unit 130 according to example 6 ofthe illumination device of the fourth embodiment of the invention;

FIG. 49 is a view showing a backlight structure according to example 7of the illumination device of the fourth embodiment of the invention;

FIG. 50 is a view showing current dependency of light emissionefficiency of an LED;

FIG. 51 is a view showing current dependency of light emission quantityof an LED;

FIG. 52 is a view showing a basic structure of an illumination deviceaccording to a fifth embodiment of the invention;

FIG. 53 is a view for explaining a first principle of a light extractionelement of the illumination device according to the fifth embodiment ofthe invention;

FIG. 54 is a view for explaining a second principle of a lightextraction element of the illumination device according to the fifthembodiment of the invention;

FIG. 55 is a view for explaining a third principle of a light extractionelement of the illumination device according to the fifth embodiment ofthe invention;

FIG. 56 is a view for explaining a fourth principle of a lightextraction element of the illumination device according to the fifthembodiment of the invention;

FIG. 57 is a block diagram showing a rough structure of a liquid crystaldisplay device according to example 5-1 of the fifth embodiment of theinvention;

FIG. 58 is a view showing a sectional structure of the liquid crystaldisplay device according to the example 5-1 of the fifth embodiment ofthe invention;

FIG. 59 is a view showing a sectional structure of a backlight unit 130of the illumination device according to the example 5-1 of the fifthembodiment of the invention;

FIG. 60 is view showing a driving method of the illumination deviceaccording to the example 5-1 of the fifth embodiment of the inventionand a liquid crystal display device using the same;

FIG. 61 is a block diagram showing a modified example of the structureof the liquid crystal display device according to the example 5-1 of thefifth embodiment of the invention;

FIG. 62 is a view showing a sectional structure of an illuminationdevice according to example 5-2 of the fifth embodiment of theinvention;

FIG. 63 is a view showing a sectional structure of an illuminationdevice according to example 5-3 of the fifth embodiment of theinvention;

FIG. 64 is a view showing a sectional structure of an illuminationdevice according to example 5-4 of the fifth embodiment of theinvention;

FIG. 65 is a view showing a sectional structure of an illuminationdevice according to example 5-5 of the fifth embodiment of theinvention;

FIG. 66 is a view showing a sectional structure of an illuminationdevice according to example 5-6 of the fifth embodiment of theinvention;

FIG. 67 is a view showing a sectional structure of the illuminationdevice according to the example 5-6 of the fifth embodiment of theinvention;

FIG. 68 is a view showing the illumination device according to theexample 5-6 of the fifth embodiment of the invention and a liquidcrystal display device using the same;

FIG. 69 is a view showing a manufacture method of an illumination deviceaccording to a sixth embodiment of the invention;

FIG. 70 is a view showing a cut wavelength change of a polarizing plateabsorption axis with respect to a heat treatment time in the heattreatment of a polarizing plate in the illumination device according tothe sixth embodiment of the invention;

FIG. 71 is a view showing a transmissivity characteristic of thepolarizing plate in an absorption axis direction in a case where thepolarizing plate is subjected to heat treatment at 70° C. in theillumination device according to the sixth embodiment of the invention;

FIG. 72 is a view showing a shrinkage ratio of the polarizing plate withrespect to the heat treatment time in the illumination device accordingto the sixth embodiment of the invention;

FIG. 73 is a view showing a relation between a thermal shock test timeand a light guide plate deformation quantity in the illumination deviceaccording to the sixth embodiment of the invention;

FIG. 74 is a view showing a section obtained by cutting a conventionaldirect type backlight unit, which is used for a TFT-LCD to support amotion picture display, along a plane orthogonal to a tube axialdirection, and a brightness distribution of illumination light from thebacklight unit;

FIG. 75 is a view showing a structure of the conventional direct typebacklight unit, which is used for the TFT-LCD to support the motionpicture display, viewed from the side of a display area;

FIG. 76 is a view showing a structure of a sidelight type backlight unitas another conventional scan type illumination device;

FIG. 77 is a schematic sectional view showing a main part of example 7-1of a seventh embodiment of the invention;

FIG. 78 is a circuit diagram showing a structure of a black displaycontrol part in a timing controller of the example 7-1 of the seventhembodiment of the invention;

FIG. 79 is a timing chart showing an operation of the example 7-1 of theseventh embodiment of the invention;

FIG. 80 is a schematic sectional view showing a main part of example 7-2of the seventh embodiment of the invention;

FIG. 81 is a circuit diagram showing a structure of a black displaycontrol part in a timing controller of the example 7-2 of the seventhembodiment of the invention;

FIG. 82 is a schematic sectional view showing a main part of example 7-3of the seventh embodiment of the invention;

FIG. 83 is a circuit diagram showing a structure of a black displaycontrol part in a timing controller of the example 7-3 of the seventhembodiment of the invention;

FIG. 84 is a schematic sectional view showing a main part of an exampleof a conventional liquid crystal display device; and

FIG. 85 is a timing chart showing an operation of the conventionalliquid crystal display device shown in FIG. 84.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

An illumination device according to a first embodiment of the inventionand a liquid crystal display device using the same will be describedwith reference to FIGS. 1 to 3. First, the rough structure of theillumination device according to this embodiment and the liquid crystaldisplay device using the same will be described with reference toFIG. 1. FIG. 1 shows a schematic state in which a TFT-LCD 1 as anexample of the display device is viewed from the side of a panel displaysurface. In an LCD panel 2, a liquid crystal 1 c is sealed between twoglass substrates, that is, an array substrate (not shown) on which TFTs4 are formed and an opposite substrate (not shown) on which commonelectrodes Ce are formed. In the illustrated LCD panel 2, an equivalentcircuit of one pixel is shown. On the array substrate, for example,plural gate bus lines 6 extending in the horizontal direction of thedrawing are formed in parallel with each other in the verticaldirection. Plural data bus lines 8 extending in the vertical directionof the drawing are formed in parallel with each other in the horizontaldirection through a not-shown insulating film. Each of pluralmatrix-shaped areas defined by the gate bus lines 6 and the data buslines 8 formed in the horizontal and vertical directions as stated aboveforms a pixel area. A pixel electrode 10 is formed in each pixel area.

A TFT 4 is formed in the vicinity of an intersection between the gatebus line 6 and the data bus line 8 in each pixel area, a gate electrodeG of the TFT 4 is connected to the gate bus line 6, and a drainelectrode D is connected to the data bus line 8. Besides, a sourceelectrode S is connected to the pixel electrode 10. The gate bus line 6is driven by a gate driver 12, and the data bus line 6 is driven by adata driver 14. Gradation voltages (gradation data) are outputted fromthe data driver 14 to the respective data bus lines 8, and when a gatesignal (gate pulse) is outputted to any one of the gate bus lines 6, aseries of TFTs 4 whose gate electrodes G are connected to the gate busline 6 are turned on. The gradation voltages are applied to the pixelelectrodes 10 connected to the source electrodes S of those TFTs 4, andthe liquid crystals 1 c are driven between the pixel electrodes and thecommon electrodes Ce formed at the opposite substrates. Besides, in eachpixel, a liquid crystal capacitance C1 c is formed of the pixelelectrode 10, the common electrode Ce and the liquid crystal 1 c, and astorage capacitance Cs is also formed in parallel with the liquidcrystal capacity C1 c.

The TFT-LCD 1 is provided with a control circuit 16 to which a clockCLK, a data enable signal Enab and a gradation data Data, which areoutputted from a system side such as a PC (Personal Computer), areinputted.

The gate driver 12 includes, for example, a shift driver, receives alatch pulse signal LP from a gate driver control part 18 in the controlcircuit 16, and sequentially outputs a gate pulse from a display startline to perform line sequential driving.

Besides, the control circuit 16 includes a display data conversioncircuit 20. The display data conversion circuit 20 has such a functionthat for example, gradation data Data to be displayed is compared withprevious gradation data Data, and when a data value is changed to exceeda specified threshold, the gradation data Data to be displayed issubjected to a specified weighting processing, and the output gradationdata is outputted to the data driver 14.

Further, the control circuit 16 includes a light source control part 22which controls an illumination device 24 for illuminating an imagedisplay area of the LCD panel 2. The illumination device 24 of thisexample uses, as an example, a direct type backlight unit. The directtype backlight unit of this embodiment includes plural (four in thisexample) divided light-emitting areas 25 to 28, and is disposed so thatthe LCD panel 2 can be illuminated from the rear surface of the displayarea. When the number of gate bus lines in one frame is L, the firstlight-emitting area 25 has an illumination range from the first gate busline 6 as the display start line to the (L/4)-th gate bus line 6.Similarly, the second light-emitting area 26 has an illumination rangefrom the (L/4+1)-th gate bus line 6 to the (2L/4)-th gate bus line 6,the third light-emitting area 27 has an illumination range from the(2L/4+1)-th gate bus line 6 to the (3L/4)-th gate bus line 6 and thefourth light-emitting area 28 has an illumination range from the(3L/4+1)-th gate bus line 6 to the L-th gate bus line 6.

Each of the light-emitting areas 25 to 28 has such a structure that alight emission opening which is substantially parallel to an extensiondirection of the gate bus line 6 is formed at a rear surface side of theLCD panel 2, and a portion other than that is surrounded by a reflectionplate or the like. In areas surrounded by the reflection plates of therespective light-emitting areas 25 to 28, for example, rod-shaped coldcathode fluorescent lamps 30 to 33, whose light emission brightness canbe changed by controlling a supplied current, are respectively disposedwhile the tube axial direction is made substantially parallel to theextension direction of the gate bus line 6. Specified driving currentsare fed to the respective cold cathode fluorescent lamps 30 to 33 fromlight source power supply circuits 35 to 38. The light source powersupply circuits 35 to 38 can give at least three stage emission statesto each of the cold cathode fluorescent lamps 30 to 33 on the basis ofcurrent control signals from the light source control part 22 of thecontrol circuit 16. Here, a first stage emission state is a non-lightingstate S1, a second stage emission state is a maximum lighting state S2in which the maximum lighting brightness is obtained, and a third stageemission state is an intermediate lighting state S3 in which about onehalf of the brightness of the second stage emission state is obtained.Incidentally, the maximum lighting brightness does not necessarily meanthe maximum brightness on specifications, which can be produced by thecold cathode fluorescent lamps 30 to 33, and also includes the highestbrightness in the brightness ranges adjusted by the light source powersupply circuits 35 to 38. A light source control system is constitutedby at least the light source control part 22 and the light source powersupply circuits 35 to 38.

The light source control part 22 of the control circuit 16 outputs thelight emission control signal to each of the light source power supplycircuits 35 to 38 in synchronization with the latch pulse signal LPoutputted to the gate driver 12 from the gate driver control part 18.Each of the light source power supply circuits 35 to 38 changes theemission state of each of the cold cathode fluorescent lamps 30 to 33 toany one of the emission states S1 to S3 on the basis of the inputtedlight emission control signal and illuminates the LCD panel 2 from therear surface of the display area.

FIG. 2 shows output timings of the gate pulses GP outputted to therespective gate bus lines 6 from the gate driver 12 in synchronizationwith the input of the latch pulse signal LP, and light emissionbrightnesses B(25) to B(28) of the respective light-emitting areas 25 to28. The horizontal direction indicates time. Here, it is assumed that asdescribed above, the L gate bus lines 6 exist in the display area andare denoted by line numbers GL(1), GL(2), . . . , GL(L−1), GL(L) insequence from the display start line.

The light source control part 22 synchronizes with the latch pulse LPfor causing the gate pulse GP(1) to be outputted to the gate bus lineGL(1) as the display start line, and outputs the light emission controlsignal for controlling the current, which is to be fed to the coldcathode fluorescent lamp 30, to the light source power supply circuit35. By this, the current fed to the cold cathode fluorescent lamp 30from the light source power supply circuit 35 is controlled, and thelight emission brightness B(25) of the light-emitting area 25 becomesthe intermediate lighting state S3 of almost one half of the maximumlighting brightness. Thereafter, until the latch pulse LP for causingthe gate pulse GP(3L/4+1) to be outputted to the gate bus lineGL(3L/4+1) is outputted, the light emission brightness B(25) of thelight-emitting area 25 is kept at the intermediate lighting state S3.

When the latch pulse LP for causing the gate pulse GP(3L/4+1) to beoutputted to the gate bus line GL(3L/4+1) is outputted, the light sourcecontrol part 22 synchronizes with it and outputs a specified lightemission control signal to the light source power supply circuit 35. Bythis, the current fed to the cold cathode fluorescent lamp 30 from thelight source power supply circuit 35 is controlled, and the lightemission brightness B(25) of the light-emitting area 25 becomes themaximum lighting state S2 in which the maximum lighting brightness isobtained. Thereafter, one frame period f is completed, a next frameperiod f is started, and until the latch pulse LP for causing the gatepulse GP(1) to be outputted to the gate bus line GL(1) is outputted, thelight emission brightness B(25) of the light-emitting area 25 is kept atthe maximum lighting state S2. Each time the next frame period f starts,the above operation is repeated.

By this illumination operation, the light emission brightness B(25) ofthe light-emitting area 25 becomes the maximum lighting state S2 only inthe ¼ frame period before the end of the one frame period f, and thearea of the ¼ frame from the top of the one frame (display area) isilluminated with the maximum brightness. For the other period of fromthe start of the one frame period f to the ¾ frame point of time, thelight emission brightness B(25) of the light-emitting area 25 is kept atthe intermediate lighting state S3, and the area of the ¼ frame from thetop of the one frame is illuminated with the intermediate brightness.

Next, when attention is paid to the light-emitting area 26, the lightsource control part 22 synchronizes with the latch pulse LP for causingthe gate pulse GP(L/4+1) to be outputted to the gate bus line GL(L/4+1)shifted from the display start line by ¼ frame, and outputs the lightemission control signal for controlling the current, which is to be fedto the cold cathode fluorescent lamp 31, to the light source powersupply circuit 36. By this, the current fed from the light source powersupply circuit 36 to the cold cathode fluorescent lamp 31 is controlled,and the light emission brightness B(26) of the light-emitting area 26becomes the intermediate lighting state S3 of almost one half of themaximum lighting brightness. Thereafter, until the latch pulse LP forcausing the gate pulse GP(1) to be outputted to the gate bus line GL(1)is outputted, the light emission brightness B(26) of the light-emittingarea 26 is kept at the intermediate lighting state S3.

When the latch pulse LP for causing the gate pulse GP(1) to be outputtedto the gate bus line GL(1) is outputted, the light source control part22 synchronizes with it and outputs a specified light emission controlsignal to the light source power supply circuit 36. By this, the currentfed from the light source power supply circuit 36 to the cold cathodefluorescent lamp 31 is controlled, and the light emission brightnessB(26) of the light-emitting area 26 becomes the maximum lighting stateS2 in which the maximum lighting brightness is obtained. Thereafter,until the latch pulse LP for causing the gate pulse GL(L/4+1) to beoutputted to the gate bus line GL(L/4+1) is outputted, the lightemission brightness B(26) of the light-emitting area 26 is kept at themaximum lighting state S2. The above operation is repeated at thefrequency of the frame period f.

By this illumination operation, the light emission brightness B(26) ofthe light-emitting area 26 becomes the maximum lighting state S2 onlyfor the first ¼ frame period of the one frame period f, and only in theperiod, the area of the ¼ frame in the range of ¼ to ½ from the top ofthe one frame is illuminated with the maximum brightness. In the periodother than that, the light emission brightness B(26) of thelight-emitting area 26 is kept at the intermediate lighting state S3,and the area of the ¼ frame in the range of ¼ to ½ from the top of theone frame is illuminated with the intermediate brightness.

Next, when attention is paid to the light-emitting area 27, the lightsource control part 22 synchronizes with the latch pulse LP for causingthe gate pulse GP(2L/4+1) to be outputted to the gate bus lineGL(2L/4+1) shifted from the display start line by the ½ frame, andoutputs the light emission control signal for controlling the current,which is to be fed to the cold cathode fluorescent lamp 32, to the lightsource power supply circuit 37. By this, the current fed from the lightsource power supply circuit 37 to the cold cathode fluorescent lamp 32is controlled, and the light emission brightness B(27) of thelight-emitting area 27 becomes the intermediate lighting state S3 ofalmost one half of the maximum lighting brightness. Thereafter, untilthe latch pulse for causing the gate pulse GP(L/4+1) to be outputted tothe gate bus line GL(L/4+1) is outputted, the light emission brightnessB(27) of the light-emitting area 27 is kept at the intermediate lightingstate S3.

When the latch pulse LP for causing the gate pulse GP (L/4+1) to beoutputted to the gate bus line GL(L/4+1) is outputted, the light sourcecontrol part 22 synchronizes with it and outputs a specified lightemission control signal to the light source power supply circuit 37. Bythis, the current fed from the light source power supply circuit 37 tothe cold cathode fluorescent lamp 32 is controlled, and light emissionbrightness B(27) of the light-emitting area 27 becomes the maximumlighting state S2 in which the maximum lighting brightness is obtained.Thereafter, until the latch pulse for causing the gate pulse GP(2L/4+1)to be outputted to the gate bus line GL(2L/4+1) is outputted, the lightemission brightness B(27) of the light-emitting area 27 is kept at themaximum lighting state S2. The above operation is repeated at thefrequency of the frame period f.

By this illumination operation, the light emission brightness B(27) ofthe light-emitting area 27 becomes the maximum lighting state S2 only inthe ¼ frame period in the range of ¼ to ½ from the head of the one frameperiod, and only in the period, the area of the ¼ frame in the range of½ to ¾ from the top of the one frame is illuminated with the maximumbrightness. In the other period, the light emission brightness B(27) ofthe light-emitting area 27 is kept at the intermediate lighting stateS3, and the area of the ¼ in the range of ½ to ¾ from the top of the oneframe is illuminated with the intermediate brightness.

Similarly, in the light-emitting area 28, the light source control part22 synchronizes with the latch pulse LP for causing the gate pulseGP(3L/4+1) to be outputted to the gate bus line GL(3L/4+1) shifted fromthe display start line by the ¾ frame, and outputs the light emissioncontrol signal for controlling the current, which is fed to the coldcathode fluorescent lamp 33, to the light source power supply circuit38. By this, the current fed from the light source power supply circuit38 to the cold cathode fluorescent lamp 33 is controlled, and the lightemission brightness B(28) of the light-emitting area 28 becomes theintermediate lighting state S3 of about one half of the maximum lightingbrightness. Thereafter, until the latch pulse LP for causing the gatepulse GP(2L/4+1) to be outputted to the gate bus line GL(2L/4+1) isoutputted, the light emission brightness B(28) of the light-emittingarea 28 is kept at the intermediate lighting state S3.

When the latch pulse LP for causing the gate pulse GP(2L/4+1) to beoutputted to the gate bus line GL(2L/4+1) is outputted, the light sourcecontrol part 22 synchronizes with it and outputs a specified lightemission control signal to the light source power supply circuit 38. Bythis, the current fed from the light source power supply circuit 38 tothe cold cathode fluorescent lamp 33 is controlled, and the lightemission brightness B(28) of the light-emitting area 28 becomes themaximum lighting state S2 in which the maximum lighting brightness isobtained. Thereafter, until the latch pulse LP for cause the gate pulseGP(3L/4+1) to be outputted to the gate bus line GL(3L/3+1) is outputted,the light emission brightness B(28) of the light-emitting area 28 iskept at the maximum lighting state. The above operation is repeated atthe frequency of the frame period f.

By this illumination operation, the light emission brightness B(28) ofthe light-emitting area becomes the maximum lighting state S2 only inthe ¼ frame period in the range of ½ to ¾ of the one frame period f, andonly in the period, the lowest stage area of the ¼ frame is illuminatedwith the maximum brightness. In the other period, the light emissionbrightness B(28) of the light-emitting area 28 is kept at theintermediate lighting state S3, and the lowest stage area of the ¼ frameis illuminated with the intermediate brightness.

By the lighting operation as described above, as shown in FIG. 2, theillumination is obtained in which the whole display area is illuminatedwith the intermediate brightness, and the light emission brightness ofthe areas obtained by longitudinally dividing the display area into fourband-shaped areas parallel to the gate bus line 6 becomes maximumsequentially in time sequence.

According to this embodiment, the display to support the motion picturecan be realized while the brightness is sufficiently suppressed to thebrightness of ⅝ (=(¼)A+¾×(½)A A: maximum lighting brightness) times asthe brightness of the conventional hold type illumination device whichis always driven by the maximum lighting brightness. Besides, since theconventional scan type illumination device to support the motion picturehas the brightness of ¼ times as the conventional hold type illuminationdevice, according to the illumination device of this embodiment, thedisplay having the high brightness of 2.5 times as the conventional scantype illumination device can be realized.

In this embodiment, although the operation example has been described inwhich the illumination having the maximum lighting brightness isperformed only in the ¼ period of the one frame period f (for example,16.7 ms), it is also possible to prolong the illumination period of themaximum lighting brightness, and by this, a higher brightness can berealized. Besides, in this embodiment, although the description has beengiven of the case where the intermediate brightness in the intermediatelighting state S3 is set to about one half of the maximum lightingbrightness, it is needless to say that the intermediate level can be setto a brightness other than that.

FIG. 3 is a graph showing, as subjective evaluations by pluralobservers, display quality when a motion picture is displayed on thedisplay area of the TFT-LCD 1 shown in FIG. 1 while an illuminationperiod at the maximum lighting brightness and an intermediate brightnesslevel are changed.

In FIG. 3, the horizontal axis indicates the ratio (%) of the maximumlighting state S2 to one frame period f, and the vertical axis indicatesthe evaluation according to evaluation points of stages 1 to 5. Theevaluation point 1 indicates a case where a motion picture blur, atailing phenomenon and the like on the motion picture display are “veryobstructive”, and the evaluation point 2 indicates a case where thosebecomes “obstructive”. The evaluation point 3 indicates a case where themotion picture blur and the like are “annoying but tolerable”, theevaluation 4 indicates a case where “a difference is seen but istolerable”, and the evaluation point 5 indicates a case where “picturequality is equivalent to a still picture and is excellent”.

In the drawing, a straight line (A) connecting circular marks indicatesa case where the bright level of the intermediate lighting state S3 isthe same as the brightness level of the maximum lighting state S2.Accordingly, irrespective of the ratio of the maximum lighting state S2to the one frame period f (hereinafter abbreviated to “the ratio of themaximum lighting state S2), the illumination with the maximum brightnesslevel is performed throughout the one frame period f. That is, thedisplay is equivalent to the hold type driving, and accordingly, thepicture image quality is such that the motion picture blur and thetailing phenomenon become very obstructive, and the evaluation point is1.

In the drawing, a polygonal line (B) connecting x marks indicates a casewhere the brightness level of the intermediate lighting state S3 isabout one half of the brightness level of the maximum lighting state S2.In this case, when the ratio of the maximum lighting state S2 is withinthe range of about 10% to 30%, the motion picture blur and the tailingphenomenon are hardly visually recognized and the excellent imagequality is obtained, and accordingly, the evaluation point is 4. Whenthe ratio of the maximum lighting state exceeds 30%, the evaluation isgradually lowered, however, the evaluation point 3 is obtained until theratio becomes about 50%.

In the drawing, a polygonal line (C) connecting triangular marksindicates a case where the brightness level of the intermediate lightingstate S3 is 30% of the brightness level of the maximum lighting stateS2. In this case, when the ratio of the maximum lighting state S2 iswithin the range of about 10% to 30%, the motion picture blur and thetailing phenomenon are hardly visually recognized and the excellentimage quality is obtained, and accordingly, the evaluation point isclose to 5. When the ratio of the maximum lighting state S2 exceeds 30%,the evaluation is gradually lowered, however, the evaluation point 3 isobtained until the ratio becomes about 50%.

In the drawing, a polygonal line (D) connecting square marks indicates acase where the brightness level of the intermediate lighting state S3 is0 (zero) and a period other than the maximum lighting state S2 becomesthe non-lighting state S1. This is the same as the illumination methodof the conventional scan type LCD. In this case, when the ratio of themaximum lighting state S2 is within the range of about 10% to 30%, themotion picture blur and the tailing phenomenon are hardly visuallyrecognized and the excellent image quality is obtained, and accordingly,the evaluation point becomes closer to 5. Besides, when the ratio of themaximum lighting state S2 exceeds 30%, the evaluation is graduallylowered, however, the evaluation point of 3 or higher is obtained untilthe ratio becomes about 50%.

From FIG. 3, it is understood that even if the brightness level of theintermediate lighting state S3 is made about 30% of the brightness levelof the maximum lighting state S2, the display quality comparable to theconventional scan type LCD indicated by the polygonal line (D) can beobtained. Further, when the brightness level of the intermediatelighting state S3 is lower than about 50% of the brightness level of themaximum lighting state S2, it is regarded as being within the allowablerange.

Besides, when the illumination time of the maximum lighting state S2 is30% or less of the one frame period f, the motion picture blur and thetailing phenomenon hardly occur, and until the illumination timeincreases up to 50%, it is regarded as being within the allowable range.

Incidentally, in this embodiment, the pixel is illuminated with themaximum brightness at the point of time when f/2 to 3f/4 has passedsince the gradation data was written into the pixel electrode 10. Thisis adopted in view of the response time of a liquid crystal molecule inthe liquid crystal 1 c to a change of electric field, and when a liquidcrystal material capable of responding at high speed is used, it is alsopossible to illuminate the pixel with the maximum brightness at thepoint of time when for example, f/4 to f/2 has passed since thegradation data was written.

As described above, the illumination device 24 of this embodiment ischaracterized in that in synchronization with the output control signal(latch pulse LP) of the gate pulse GP, the illumination device switchesbetween the maximum lighting state S2 and the intermediate lightingstate S3.

Besides, the illumination device 24 of this embodiment performs such acontrol that the gate pulse GP is outputted to the gate bus line 6, theTFT 4 connected to the gate bus line 6 is turned on, the gradation datais written into the pixel electrode 10, and in a period when the liquidcrystal molecule of the liquid crystal 1 c is performing an inclinationoperation by this to a desired inclination angle, the intermediatelighting state S3 is kept, and when the inclination response of theliquid crystal molecule is almost completed, the maximum lighting stateS2 is made to occur. By doing so, it is possible to solve the problem ofthe conventional scan type LCD in which as the maximum lighting state S2becomes short, the picture quality degradation such as the movement blurcan be improved, however, since the period other than the state S2 iskept at the non-lighting state S1, the brightness of the display screenbecomes low. In the illumination device 24, even if the time of themaximum lighting state S2 is short, since the illumination is continuedat the specified intermediate brightness level by the intermediatelighting state S3, it is possible to lessen the drop of the brightness.

The picture quality degradation such as the movement blur is suppressedby using the illumination device 24 because the illumination methodthereof skillfully uses a human engineering feature that the human eyesenses a change with emphasis. That is, the human eye senses an image atthe instant when the intermediate lighting state S3 is changed to themaximum lighting state S2, and brands it on the retina. This imagerecognition operation is performed every frame, and the visualrecognition of the movement blur and the tailing phenomenon isprevented. On the other hand, since a human being senses the integrationvalue of incident light to the retina as the brightness, an average ofthe light quantity at the intermediate lighting state S3 and the lightquantity at the maximum lighting state becomes the brightness of thedisplay area of the TFT-LCD 1.

By using this embodiment, a liquid crystal display device having highbrightness and less movement blur can be realized with a simple and thinstructure, and the invention can contribute to the improvement indisplay quality, the reduction in cost of the device, and theminiaturization.

In the above embodiment, although the description has been given of thescan type illumination device in which one frame is divided into fourparts, the structure and the method of the embodiment can be applied toany case where one frame is divided into N parts (N is an integer of 1or larger). For example, in the case of N=1, in a period when gradationdata is being written into all pixels of the display area of the LCDpanel 2, the whole is illuminated in the intermediate lighting state S3,and after a specified liquid crystal response time has passed since thepixel writing of the final line, the whole is illuminated in the maximumlighting state S2. The maximum lighting state S2 is realized in, forexample, a vertical blanking period. By doing so, one cold cathodefluorescent lamp (light source) is used and the TFT-LCD can be realizedin which the motion blur and the tailing phenomenon are reduced whilethe drop of brightness is suppressed.

Besides, in the above embodiment, although the description has beengiven of the direct type backlight unit as an example, the invention isnot limited to this, and the structure and method of this embodiment maybe naturally applied to a sidelight type backlight unit in which a lightsource is disposed at the end of a light guide plate.

Incidentally, the illumination driving method in the illumination device24 used in this embodiment may be naturally applied to a driving methodof, for example, an EL (Electro Luminescence) display device (using anorganic EL element or an inorganic EL element) as a self-luminous planedisplay device.

Second Embodiment

An illumination device according to a second embodiment of the inventionand a liquid crystal display device using the same will be describedwith reference to FIGS. 4 to 8. First, a rough structure of theillumination device according to this embodiment and the liquid crystaldisplay device using the same will be described with reference to FIGS.4, 5A and 5B. FIG. 4 shows the rough structure of the illuminationdevice according to this embodiment and the liquid crystal displaydevice using the same. A TFT-LCD 1 shown in FIG. 4 is the same as theTFT-LCD 1 of the first embodiment explained by use of FIG. 1, andstructural elements having the same operation and function are denotedby the same symbols, and the description will be omitted. FIG. 5A is asectional view taken along line A-A of FIG. 4 and shows a sectionobtained by cutting an illumination device (sidelight type backlightunit) 40, which is used for the TFT-LCD 1 to support the motion picturedisplay according to this embodiment, along a plane orthogonal to a tubeaxial direction of a cold cathode fluorescent lamp. FIG. 5B shows abrightness distribution of illumination light from the illuminationdevice 40 at the rear surface side of a display area of the TFT-LCD 1.

The illumination device 40 of this embodiment is a sidelight typebacklight unit which has a structure for emitting internally guidedlight to the outside and in which cold cathode fluorescent lamps aredisposed along the end of a light guide plate. The sidelight typebacklight unit of this example includes plural (four in this example)divided light-emitting areas 41 to 43, and is disposed so that an LCDpanel 2 can be illuminated from the rear surface of the display area.

When the number of gate bus lines in one frame is L, the firstlight-emitting area 41 has an illumination range of from the first gatebus line 6 as the display start line to the (L/4)-th gate bus line 6.Similarly, the second light-emitting area 42 has an illumination rangeof from the (L/4+1)-th gate bus line 6 to the (2L/4)-th gate bus line 6,the third light-emitting area 43 has an illumination range of from the(2L/4+1)-th gate bus line 6 to the (3L/4)-th gate bus line 6 and thefourth light-emitting area 44 has an illumination range of from the(3L/4+1)-th gate bus line 6 to the L-th gate bus line 6.

As shown in FIG. 5A, two light guide plates 51 and 52 are disposed onsubstantially the same plane at the side facing the rear surface of theTFT-LCD 1. The light guide plate 51 is disposed in the first and thesecond light-emitting areas 41 and 42, and the light guide plate 52 isdisposed in the third and the fourth light-emitting areas 43 and 44. Acold cathode fluorescent lamp 46 is disposed at an end of the lightguide plate 51 opposite to an end facing the light guide plate 52, and acold cathode fluorescent lamp 47 is disposed at an end of the lightguide plate 52 opposite to an end facing the light guide plate 51.

Besides, a light guide plate 50 is disposed in the first light-emittingarea 41 and to be adjacent to a surface of the light guide plate 51 atthe side opposite to the side of the TFT-LCD 1. A cold cathodefluorescent lamp 45 is disposed at one end of the light guide plate 50.A light guide plate 53 is disposed in the fourth light-emitting area 44and to be adjacent to a surface of the light guide plate 52 at the sideopposite to the side of the TFT-LCD 1. A cold cathode fluorescent lamp48 is disposed at an end of the light guide plate 53. The cold cathodefluorescent lamps 45 to 48 are formed into, for example, linear rodshapes. Besides, the light emission brightnesses of the cold cathodefluorescent lamps 45 to 48 can be changed by controlling the suppliedcurrent.

Specified driving currents are fed from light source power supplycircuits 35 to 38 to the respective cold cathode fluorescent lamps 45 to48. The respective light source power supply circuits 35 to 38 can giveat least three stage emission states to the respective cold cathodefluorescent lamps 45 to 48 on the basis of current control signals froma light source control part 22 of a control circuit 16. Here, a firststage emission state is a non-lighting state S1, a second stage emissionstate is a maximum lighting state S2 in which maximum lightingbrightness is obtained, and a third stage emission state is anintermediate lighting state S3 in which about one half of the brightnessof the second stage emission state is obtained. Here, the maximumlighting brightness does not necessarily mean the maximum brightness onspecifications, which can be produced by the cold cathode fluorescentlamps 45 to 48, and also includes the highest brightness in thebrightness range adjusted by the light source power supply circuits 35to 38.

The illumination device 40 according to this embodiment as describedabove is constructed such that a light source unit (50, 45) includingthe light guide plate (light guiding member) 50 and the cold cathodefluorescent lamp 45 disposed at the end thereof and for emitting lightfrom one surface is laminated on a light source unit (51, 46) includingthe light guide plate 51 and the cold cathode fluorescent lamp 46disposed at the end thereof. Besides, the illumination device 40 isconstructed such that a light source unit (53, 48) including the lightguide plate 53 and the cold cathode fluorescent lamp 48 disposed at theend thereof and for emitting light from one surface is laminated on alight source unit (52, 47) including the light guide plate 52 and thecold cathode fluorescent lamp 47 disposed at the end thereof. Further,the illumination device 40 is constructed such that the light sourceunit (51, 46) and the light source unit (52, 47) are disposed on thesame plane. Besides, the illumination device 40 is constructed such thatthe light source unit (50, 45) and the light source unit (53, 48) aredisposed on the same plane.

Each of the light-emitting areas 41 to 44 is constructed such that alight emission opening is formed at the rear side of the LCD panel 2,and a portion other than that is surrounded by a diffuse reflectionplate 55. A diffusion sheet 60 is disposed between the rear surface ofthe TFT-LCD 1 and the light emission opening of the illumination device40. As light extraction structures 56 to 59, for example, lightscattering patterns are printed on the rear surface of the light guideplate 50 in the first light-emitting area 41, the rear surface of thelight guide plate 51 in the second light-emitting area 42, the rearsurface of the light guide plate 52 in the third light-emitting area 43,and the rear surface of the light guide plate 53 in the fourthlight-emitting area 44. A light extraction structure is not formed onthe rear surface of the light guide plate 51 in the first light-emittingarea 41 and the rear surface of the light guide plate 52 in the fourthlight-emitting area 44.

By the arrangement of the light extraction structures 56 and 57, most ofthe light from the cold cathode fluorescent lamp 45 is guided throughthe light guide plate 50 while being scattered by the light extractionstructure 56, and further passes through the portion of the firstlight-emitting area 41 of the light guide plate 51 and is emitted fromthe first light-emitting area 41. At this time, part of the light isguided through the light guide plate 51, is scattered by the lightextraction structure 57, and is emitted from the second light-emittingarea 42. Further, part of the light is guided from the light guide plate51 to the light guide plate 52 and the light guide plate 53, isscattered by the light extraction structures 58 and 59, and is emittedfrom the third and the fourth light-emitting areas 43 and 44. That is,most of the light from the cold cathode fluorescent lamp 45 is used forthe illumination of the first light-emitting area 41, and the remainderis used for the illumination of the second to the fourth light-emittingareas 42 to 44.

Similarly, most of the light from the cold cathode fluorescent lamp 46is guided through the light guide plate 51, and is emitted from thesecond light-emitting area 42 while being scattered by the lightextraction structure 57. At this time, part of the light is guided tothe light guide plates 50, 52 and 53, is scattered by the lightextraction structures 56, 58 and 59, and is emitted from the firstlight-emitting area 41, and the third and the fourth light-emittingareas 43 and 44. That is, most of the light from the cold cathodefluorescent lamp 46 is used for the illumination of the secondlight-emitting area 42, and the remainder is used for the illuminationof the first light-emitting area 41, and the third and the fourthlight-emitting areas 43 and 44.

On the other hand, by the arrangement of the light extraction structures58 and 59, most of the light from the cold cathode fluorescent lamp 48is guided through the light guide plate 53 while being scattered by thelight extraction structure 59, and further passes through the portion ofthe fourth light-emitting area 44 of the light guide plate 52 and isemitted from the fourth light-emitting area 44. At this time, part ofthe light is guided through the light guide plate 52, is scattered bythe light extraction structure 58, and is emitted from the thirdlight-emitting area 43. Further, part of the light is guided from thelight guide plate 52 to the light guide plate 51 and the light guideplate 50, is scattered by the light extraction structures 57 and 56 andis emitted from the second and the first light-emitting areas 42 and 41.That is, most of the light from the cold cathode fluorescent lamp 48 isused for the illumination of the fourth light-emitting area 44, and theremainder is used for the illumination of the first to the thirdlight-emitting areas 41 to 43.

Similarly, most of the light from the cold cathode fluorescent lamp 47is guided through the light guide plate 52, and is emitted from thethird light-emitting area 43 while being scattered by the lightextraction structure 58. At this time, part of the light is guided tothe light guide plates 50, 51 and 53, is scattered by the lightextraction structures 56, 57 and 59, and is emitted from the firstlight-emitting area 41, the second light-emitting area 43 and the fourthlight-emitting area 44. That is, most of the light from the cold cathodefluorescent lamp 47 is used for the illumination of the thirdlight-emitting area 43, and the remainder is used for the illuminationof the first and the second light-emitting areas 41 and 42, and thefourth light-emitting area 44.

The light source control part 22 of the control circuit 16 shown in FIG.4 synchronizes with the latch pulse signal LP outputted to the gatedriver 12 from the gate driver control part 18 and outputs the lightemission control signal to the respective light source power supplycircuits 35 to 38. Each of the light source power supply circuits 35 to38 changes the emission state of each of the cold cathode fluorescentlamps 41 to 44 to any one of the first to the third emission states S1to S3, and the LCD panel 2 is illuminated from the rear surface of thedisplay area.

In the structure as stated above, illumination driving similar to thatof the first embodiment shown in FIG. 2 is performed. In thisembodiment, the light emission brightnesses B(25) to B(28) of FIG. 2 areread as light emission brightnesses B(41) to B(44).

The light source control part 22 synchronizes with the latch pulse LPfor causing the gate pulse GP (1) to be outputted to the gate bus lineGL(1) as the display start line, and outputs the emission control signalfor controlling the current, which is to be fed to the cold cathodefluorescent lamp 45, to the light source power supply circuit 35. Bythis, the current fed from the light source power supply circuit 35 tothe cold cathode fluorescent lamp 45 is controlled, and the lightemission brightness B(41) of the light-emitting area 41 becomes theintermediate lighting state S3 of about one half of the maximum lightingbrightness. Thereafter, until the latch pulse LP for causing the gatepulse GP(3L/4+1) to be outputted to the gate bus line GL(3L/4+1) isoutputted, the light emission brightness B(41) of the light-emittingarea 41 is kept the intermediate lighting state S3.

When the latch pulse LP for causing the gate pulse GP(3L/4+1) to beoutputted to the gate bus line GL(3L/4+1) is outputted, the light sourcecontrol part 22 synchronizes with it and outputs a specified lightemission control signal to the light source power supply circuit 35. Bythis, the current fed from the light source power supply circuit 35 tothe cold cathode fluorescent lamp 45 is controlled, and the lightemission brightness B(41) of the light-emitting area 41 becomes themaximum lighting state S2 in which the maximum lighting brightness isobtained. Thereafter, one frame period f is completed, a next frameperiod f is started, and until the latch pulse LP for causing the gatepulse GP(1) to be outputted to the gate bus line GL(1) is outputted, thelight emission brightness B(41) of the light-emitting area 41 is keptthe maximum lighting state S2. Each time the next frame period f isstarted, the above operation is repeated.

By this illumination operation, the light emission brightness B(41) ofthe light-emitting area 41 becomes the maximum lighting state S2 only inthe ¼ frame period before the end of the one frame period f, and thearea of the ¼ frame from the top of the one frame (display area) isilluminated with the maximum brightness. In the other period from thestart of the one frame period f to the ¾ frame point of time, the lightemission brightness B(41) of the light-emitting area 41 is kept theintermediate lighting state S3, and the area of the ¼ frame from the topof the one frame is illuminated with the intermediate brightness.

Similarly to the description of the first embodiment, the emissionoperations in the light-emitting areas 42, 43 and 44 are performed, andas shown in FIG. 2, the illumination is obtained in which the wholedisplay area is illuminated with the intermediate brightness, and thelight emission brightnesses of the areas obtained by longitudinallydividing the display area into four band-shaped areas parallel to thegate bus line 6 become maximum sequentially in time sequence. Althoughthis description has been given of the example in which the maximumlighting state S2 and the intermediate lighting state S3 are switched,the same effect can also be obtained when the maximum lighting state S2and the non-lighting state S1 are switched.

Besides, in this embodiment, although the description has been given ofthe structure that the two light guide plates are laminated, and twosuch pairs are disposed in the plane, the same effect can also beobtained when the number of laminated plates is increased. Besides, inthe structure shown in FIG. 5A, when the light source power supplycircuits 35 to 38 and the like are disposed in recess parts (rearsurface of the light-emitting areas 42 and 43) of the backlight, or thecold cathode fluorescent lamps 45 and 48 are disposed therein, thereduction in thickness of the device and the miniaturization can berealized.

As stated above, although the illumination device 40 according to thisembodiment is of the sidelight type, the light source unit for mainlyilluminating one light-emitting area supplies part of the light to theother adjacent light-emitting area, and on the other hand, the lightsource unit for illuminating the other light-emitting area supplies partof the light to the one adjacent light-emitting area, and mutualcompensation can be made, and accordingly, as shown in FIG. 5B, auniform brightness distribution α can be realized. Besides, the lightsource is disposed at the end face of each light guide member, andlighting and non-lighting of this light source, or lighting anddarkening thereof are individually controlled, so that the illuminationdevice of the liquid crystal display device suitable for motion picturedisplay can be realized to be thin.

Next, a modified example of the illumination device 40 according to thisembodiment and the TFT-LCD 1 using the same will be described withreference to FIGS. 6A and 6B. The structure shown in FIG. 6A is the sameas the structure shown in FIG. 5 except that a structure of anillumination device 40 partially varies. The illumination device 40shown in FIG. 6 has a feature that a light mixing area 62 is providedbetween a diffusion sheet 60 and light guide plates 51 and 52 oflaminated light source units at a side of a TFT-LCD 1.

The light mixing area 62 is formed of a transparent plate made of acrylor polycarbonate, a diffused plate in which a minute material havingdifferent refractivity, such as a fiber, is mixed in the transparentplate or an air layer. When the air layer of a space of 0.5 mm to 10 mmis used, as compared with a brightness distribution α (identical to thebrightness distribution a of FIG. 5B) in the case where the air layerdoes not exist and indicated by a broken line of FIG. 6B, a brightnessdistribution β indicated by a solid line is obtained in which brightnessirregularity at a boundary portion of the light-emitting areas isrelieved, and a brightness change is not visually recognized.

According to this embodiment, minute brightness changes at the boundaryof the light-emitting areas are mutually mixed, and transversal-shapeduneven brightness, which was visually recognized at the boundaryportion, can be relieved or eliminated.

Incidentally, in the illumination device 40 shown in FIGS. 5A and 6A,although all the light extraction structures 56 to 59 of the light guideplates 50 to 53 are disposed at the lower side of the light guide plates50 to 53, when the light extraction structures 56 and 59 of the firstand the fourth light-emitting areas 41 and 44 are disposed on the uppersurfaces of the light guide plates 50 and 53, the light extractionstructures 56 to 59 are disposed on the one plane so that the brightnesscan be made further uniform.

Next, a modified example of the illumination device of this embodimentwill be described with reference to FIGS. 7A to 7C. The structure shownin FIG. 7A is the same as the structure shown in FIG. 5A except that astructure of an illumination device 40 partially varies. Theillumination device 40 shown in FIG. 7A has a feature that adouble-sided reflection member 64 to perform regular reflection ordiffuse reflection as shown in FIG. 7B or 7C is disposed in a gapbetween light guide plates 51 and 52. At the boundary portion of thesecond and the third light-emitting areas 42 and 43 of the illuminationdevice 40 shown in FIGS. 5A and 6A, part of the light is reflectedtoward the side of the light source by surface reflection at the endface of the light guide plate, and is again guided and the remainder isemitted from the end face and is incident on the other illuminationarea. Thus, there is a possibility that emitted lights are mixed and themotion picture performance is degraded. Then, the double-sidedreflection plate 64 is disposed in the gap between the light guideplates 51 and 52. By this, the mixture of the emitted lights isprevented, and the motion picture performance can be improved.

FIG. 7B shows such a structure that the opposite end faces of the lightguide plates 51 and 52 face with each other in parallel and aresubstantially orthogonal to the light emission surfaces of the lightguide plates 51 and 52, and the double-sided reflection member 64 madeof a double-sided regular reflection plate or a double-sided regularreflection sheet is disposed in the gap.

FIG. 7C shows such a structure that a Λ-shaped gap opening to the rearsurface side is provided at the opposite end faces of the light guideplates 51 and 52, and the double-sided reflection member 64 made of adouble-sided regular reflection plate or a double-sided regularreflection sheet is disposed in the gap. Since the double-sidedreflection member 64 shown in FIG. 7B has a finite thickness, whenviewed from the light emission side (side of the TFT-LCD 1) of the lightguide plates 51 and 52, the gap is visually recognized as a shadow andthe uneven brightness is produced. On the other hand, when the structureas shown in FIG. 7C is adopted, the double-sided reflection member 64 isnot seen from above, and the effect of improving the uneven brightnessis obtained. Incidentally, even when the structure is adopted such thatthe light guide plates are in contact with each other in the vicinity ofthe Λ-shaped apex, a sufficiently superior effect with respect to themotion picture performance can be obtained.

When the refractivity of the light guiding material is n, it ispreferable that the apex angle θ of the Λ-shaped double-sided reflectionmember 64 satisfies θ≦180°−4×sin⁻¹(1/n) . . . (expression 1). In thecase where the apex angle of the Λ shape is larger than θ of the aboveexpression, part of the light guided through the light guide plate andreflected at the end face is emitted upward from the light guide plate.Thus, there is a case where linear clear unevenness occurs on the liquidcrystal panel plane. Accordingly, when the apex angle θ satisfying theabove expression 1 is adopted, since the end face reflected light isentirely guided, it becomes possible to prevent the uneven brightness.

The expression 1 will be described with reference to FIGS. 8A and 8B.FIG. 8A is an enlarged view of FIG. 7C, and FIG. 8B shows the course oflight at the end face on the side of the light guide plate 52. In FIG.8B, the emission light of the light guide plate 52 is composed of lightbeams scattered by the printed scattering pattern of the lightextraction structures 58 of the lower surface of the light guide plate52, and when the incident light from the end face A is emitted to thelight-emitting area from the light guide plate 52, only a portion withinthe reach of the light beam from the end face A comes to have highbrightness, and the uneven brightness occurs.

The apex angle θ is determined by the condition that the incident lightbeam from the end face A is not emitted from the emission surface of thelight guide plate 52. Here, the incident angle of the light beamincident on the end face A is made a, the refraction angle of the lightbeam incident on the light guide plate 52 from the end face A is made b,the incident angle of the light beam incident from the end face A on thelight-emitting area opening surface of the light guide plate 52 is madec, and the refractivity of the light guide plate 52 is made n. Theincident light from the Λ-shaped end face A of the light guide plate 52is refracted according to Snell's law.sin(a)=n×sin(b)  (1)n×sin(c)=sin(d)  (2)

Besides, the refraction angle b and the incident angle c are expressedby the following expression.90°=b+c+θ/2  (3)

Here, if d≧90°, light incident on the light guide plate 52 from the endface A is not emitted from the light guide plate 52.

(4) Besides, since there is a possibility of incidence from anydirection, the incident angle a becomes ±90°.

The expression (1) can be modified to b=sin⁻¹(1/n), and the expression(2) can be modified to c=sin⁻¹(1/n).

When these are substituted into the expression (3),θ=180°−4×sin⁻¹(1/n)

From the condition of (4),θ≦180°−4×sin⁻¹(1/n).

For example, in the case of PMMA of a normal light guide plate material,n=1.48, and accordingly, θ=9.97°.

Next, still another modified example of the illumination device of thisembodiment will be described with reference to FIGS. 9A to 9C. Thestructure shown in FIG. 9B is the same as the structure shown in FIG. 5Aexcept that a structure of an illumination device 40 partially varies.FIG. 9A shows a rough structure of the illumination device of thismodified example and a liquid crystal display device using the same. ATFT-LCD 1 shown in FIG. 9A is the same as the TFT-LCD 1 of thisembodiment explained by use of FIG. 4, and structural elements havingthe same operation and function are denoted by the same symbols and thedescription will be omitted. FIG. 9B is a sectional view taken alongline A-A of FIG. 9A, and shows a section obtained by cutting theillumination device (sidelight type backlight unit) 40, which is usedfor the TFT-LCD 1 to support the motion picture display according tothis embodiment, along a plane orthogonal to a tube axial direction of acold cathode fluorescent lamp. FIG. 9C shows a brightness distributionof illumination light from the illumination device 40 at the rearsurface side of a display area of the TFT-LCD 1.

The structure shown in FIG. 9A is the same as the structure shown inFIG. 4 except that the structure of the illumination device 40 partiallyvaries. The illumination device 40 shown in FIG. 9A has a feature thatbrightness adjusting volumes 70 to 73 are provided for light sourcepower supply circuits 35 to 38, respectively, and the quantities ofemission lights from respective light-emitting areas 41 to 44 can befinely adjusted and can be made uniform.

Originally, the emission light quantities of the cold cathodefluorescent lamps are different from each other. Thus, there can arise aproblem that the brightnesses of the first to the fourth light-emittingareas 41 to 44 are different from each other. As a countermeasureagainst this problem, it is conceivable that the brightness of each ofthe cold cathode fluorescent lamps is evaluated, and the cold cathodefluorescent lamps having the same brightness are combined and used,however, there is a problem that the manufacturing cost becomes high. Onthe other hand, according to this structure, the uneven brightness islowered at low cost, and the display surface brightness can be madeuniform.

As described above, according to this embodiment, the liquid crystaldisplay device which can obtain the uniform brightness distribution andis suitable for the motion picture display can be manufactured to besmall and thin.

Third Embodiment

An illumination device according to a third embodiment of the inventionand a liquid crystal display device using the same will be describedwith reference to FIGS. 10A to 29 and FIG. 1 showing the firstembodiment. This embodiment has been made to solve the problem of thethird related art, and realizes a display device in which even if alighting period of a cold cathode fluorescent lamp of an illuminationdevice is made short, light emission brightness of the cold cathodefluorescent lamp is not required to be raised, and a high quality motionpicture image can be obtained.

Subjective evaluation was performed as to whether or not a difference inpicture quality was felt in the case where a ratio (duty rate) of alighting time of a backlight unit in one frame period was changed, andfurther, gradation data was processed and transmissivity of liquidcrystal was adjusted. It has been found that even if the duty ratio isthe same, according to image data, a difference in picture quality fromthe original image is felt or is not felt. Examples of the subjectiveevaluation result are shown in FIGS. 10A and 10B. FIG. 10A shows thesubjective evaluation result at a duty ratio of 80%, and FIG. 10B showsthe subjective evaluation result at a duty ratio of 60%. The horizontalaxis of FIGS. 10A and 10B indicates an average value of all gradationdata of 64 gradations of 0 to 63 displayed on one frame. The verticalaxis indicates a ratio (%) of the number of pixels saturated inbrightness by processing of image data to the number of total displaypixels. When the number of high brightness pixels saturated inbrightness by adjustment of the transmissivity of the liquid crystal isexamined, it varies according to the content of the image, and at boththe duty ratio of 80% and the duty ratio of 60%, when the ratio of thenumber of pixels saturated in brightness to the number of all displaypixels is 2% or less of the whole display, the difference in picturequality from the original image is not felt irrespective of the averagevalue (average brightness of the image) of all gradation data of theimage. Although individual illustration is omitted, it has been foundthat when the ratio of the pixels saturated in brightness is 2% or lessof the whole, even if the duty ratio is lowered, the difference inpicture quality from the original image is not felt in any image.

From the above, pixels at a specified ratio and selected in descendingorder of brightness in an image are made to have the maximum displaybrightness, and the respective brightnesses of the remaining pixelsexcept for those are reproduced by lowering the duty ratio of the lightsource of the backlight unit and raising the transmissivity of theliquid crystal, so that it becomes possible to make the quality of themotion picture display equivalent to the original image even if the dutyratio is lowered.

The liquid crystal display device according to this embodiment has thesame structure as the structure described in the first and the secondembodiments and shown in FIGS. 1 and 4. The same structural elements asthose of FIGS. 1 and 4 are denoted by the same symbols and the detaileddescription will be omitted. A TFT-LCD 1 includes an LCD panel 2 tomodulate light transmissivity of respective sub-pixels of red (R), green(G) and blue (B), which are two-dimensionally arranged in a matrix form,on the basis of gradation data. An illumination device 24 (or anillumination device 40, hereinafter, the description will be given usingthe illumination device 24) for irradiating light is provided at therear surface of a display area of the LCD panel 2. The illuminationdevice 24 includes light sources (cold cathode fluorescent lamps 30 to33) and light source power supply circuits 35 to 38 for driving them.

A control circuit 16 of this embodiment is provided with variouscircuits for driving the TFT-LCD 1, and a display data conversioncircuit 20 for analyzing gradation data inputted from the outside. FIG.11 shows a rough operation procedure of the display data conversioncircuit 20. As shown in FIG. 11, the display data conversion circuit 20stores the gradation data of pixels (combination of sub-pixels of R, Gand B) of one frame inputted to the control circuit 16 (step S1),obtains lightness Y=r×R+g×G+b×B (r, g and b are real numbers including anumerical value of 0) from the respective gradation data (R, G, B)corresponding to the respective pixels (step S2), and creates ahistogram of the lightness Y of the image (step S3). Next, the number Mof pixels relating to an image display in one frame is calculated (stepS4), a specific number t=M×p of a product of the number M of pixels anda specified brightness saturation ratio p (step S5), and thresholdlightness Yα is determined from the histogram of the lightness Y of theimage and the specific number t (step S6). Next, the processed gradationdata is outputted to the plural data bus lines 8 on the basis of thethreshold lightness Yα (step S7), and specified duty ratio data isoutputted to the light source control part 22 for controlling the lightsource power supply circuits 35 to 38 (step S8). The light sourcecontrol part 22 controls the light source power supply circuits 35 to 38on the basis of the duty ratio data, and turns on the cold cathodefluorescent lamps 30 to 33 at the specified duty ratio.

For example, the display data conversion circuit 20 determines the dutyratio so that the product of the maximum value which the lighttransmissivity can take (maximum value which the gradation data cantake) and the illumination quantity (duty ratio) of the illuminationdevice 24 becomes equal to the threshold lightness Yα, the gradationdata of the pixels of the lightness Y higher than the thresholdlightness Yα is processed so that the light transmissivity comes to havethe maximum value, and in the other pixel, the gradation data isprocessed so that the product of the processed gradation data and thedetermined duty ratio becomes equal to the lightness Y of the originalgradation data of the pixel.

FIG. 12 is a flowchart showing a calculation of the lightness Y in thedisplay data conversion circuit 20 and a procedure of histogramcreation. The display data conversion circuit 20 sequentially readsgradation data D (R, G, B) of one frame stored in a not-shown storagedevice (memory) (steps S10 and S11), sets a constant to be, for example,(r, g, b)=(0.2126, 0.7152, 0.0722), and calculates the lightnessY=r×R+g×G+b×B for the read gradation data (R, G, B) (step S12). Next, avariable s is set to 63 (step S13), and the values of Y and s arecompared with each other (step S14). If Y≈s, the procedure proceeds tostep S15, 1 is subtracted from the value of s, the comparison of the Yvalue and the value is performed again at the step S14, and the stepsS14 and S15 are repeated until Y=s is established. If Y=s, the procedureproceeds to step S16, 1 is added to a frequency L(s) indicating thenumber of times of appearance of the lightness Y=s in one frame, and theprocedure returns to the step S10. For example, when the gradation data(R, G, B)=(58, 30, 25) is read at the step S11, the lightness Y=35 iscalculated at the step S12, and 1 is added to the value of the frequencyL(35) indicating the number of times of appearance of the lightness Y=35in one frame (step S16). The procedure from the step S10 to the step S16is repeated by the number of gradation data of one frame, so that therespective values of the frequencies L(0) to L(63) of the lightness Y=0to 63 in the one frame are obtained, and the histogram L of thelightness Y is calculated.

FIG. 13 is a flowchart showing a procedure for calculating the number Mof pixels which an image occupies in the case where the image existsonly in a part of one frame (screen). Pixels of two-dimensionalarrangement are made to have m rows and n columns, and it is assumedthat when the lightness Y of gradation data (R, G, B) at an i-th row anda j-th column is 0 (that is, black display in a normally black mode),x(i)=y(j)=0 is made to be satisfied at a pixel (x(i), y(i)), and in theother case, x(i)=y(j)=1 is made to be satisfied. With respect to allpixels of the one frame, a comparison between the lightness Y and thevalue 0 is made, and x(i)=y(j)=0 or x(i)=y(j)=1 is substituted into acoordinate (x(i), y(i)) of each pixel. Since the image is almost square,when all pixels in a vertical or horizontal column or row become black(a pixel which becomes black display has x(i)=y(j)=0), they are regardedas a background, and the other pixels are selected as the image and thenumber M is obtained. That is, the number of pixels of x(i)=1 and thenumber of pixels of y(i)=1 are calculated, and the product of both isobtained, so that the number M is obtained. For example, in the casewhere pixels for display exist substantially in the center of the frame,among pixels of xm rows and yn columns in the whole frame, the number Mof pixels is obtained in a range except for x1 to xb rows, xc to xmrows, y1 to yf columns and yg to yn columns in which all image signalsare 0.

Specifically, in all i and j, from a state of x(i)=y(j) 0, at step S20of FIG. 13, variables are set to be i=1 and j=1, the variable j=1 and acolumn value (n+1) are compared with each other (step S21). If j=1<n+1,since reading of data is not performed up to the final column n, theprocedure proceeds to step S22, and the lightness Y of a pixel (1, 1) ofthe first row and the first column is read. Next, the read lightness Yand the value 0 (zero) are compared with each other (step S23), and ifY>0, since gradation data other than black exists in the pixel (1, 1),the procedure proceeds to step S24, x(1) is set to the value 1, y(1) isset to the value 1, and the procedure proceeds to step S25. In the caseof Y=0, the procedure proceeds to step S25 without executing the stepS24. In this case, the pixel remains x(1) y(1)=0.

Next, at the step S25, the variable i=1 and the row value m are comparedwith each other. If i=1<m, since data reading is not performed up to thefinal row m, the value of i is increased by one (step S26), theprocedure again returns to the step S21, the lightness Y of a next pixel(2, 1) is read, the lightness Y and the value 0 are compared with eachother (step S23), and if Y>0, the setting of x(2)=1 and y(1)=1 is madeat (x(2), y(1)) (step S24). By repeating this operation up to i=m, theprocessing of the m pixels at the column j=1 is ended.

Next, the procedure proceeds to step S27 from the step S25, the value ofi is set to the initial value 0, the value of the variable j isincreased by one, the procedure again returns to the step S21, and thelightness Y of the pixel (1, 2) at the first row and the second columnis read. Next, the read lightness Y and the value 0 (zero) are comparedwith each other (step S23), and if Y>0, since gradation data other thanblack exists in the pixel (1, 2), the procedure proceeds to the stepS24, x(1) of (x(1), y(2)) is set to the value 1, y(2) is set to thevalue 1, and the procedure proceeds to step S25. In the case of Y=0, theprocedure proceeds to step S25 without performing the step S24. In thiscase, the pixel remains x(1)=y(2)=0.

Next, at the step S25, the variable i=1 and the row value m are comparedwith each other. If i=1<m, since data reading is not performed up to thefinal row m, the value of i is increased by one (step S26), theprocedure again returns to the step S21, the lightness Y of the nextpixel (2, 2) is read, and the lightness Y and the value 0 are comparedwith each other (step S23), and if Y>0, the setting of x(2)=1 and y(2)=1is made (step S24). By repeating this operation up to i=m, theprocessing of the m pixels at the column j=2 is ended. The aboveoperation is repeated and when the variable j becomes j=n+1 at the stepS21, the procedure proceeds to a “judgment” routine.

In the “judgment” routine, after i=0 and j=0 are set at step S28, thevalue of i is increased by one at step S29, and the value of x(i) isadded to the variable x (step S30). This processing is repeated up toi=m (row) (step S31), and when the value becomes i=m, the procedureproceeds to step S32. By the processing up to the step S31, the number xof pixels used for the image display in the row direction is grasped.

Next, the value of j is increased by one at the step S32, and the valueof y(j) is added to the variable y (step S33). This processing isrepeated up to j=n (column) (step S34), and the procedure proceeds tostep S35 when j=n is obtained. By the processing up to the step S34, thenumber y of pixels used for the image display in the column direction isgrasped.

Next, at the step S35, the product of the number x of image displaypixels in the row direction and the number y of image display pixels inthe column direction are obtained, and the number M of image displaypixels of the one frame is obtained.

FIG. 14 is a flowchart showing a procedure for calculating the thresholdlightness Yα. In this procedure, on the basis of the number M of imagedisplay pixels and a specified number p, the lightness Y lower than thehighest lightness by t=Mp pixels in sequence is made the thresholdlightness Yα. The specified number p indicates the ratio of pixelssaturated in brightness by image processing, and from the subjectiveevaluation result shown in FIG. 10, it is preferable that the number pis p=0.02 (=2%) or less. When the specified number p is 2%, and thenumber M of image display pixels is 80000, the specified numbert=Mp=80000×2 (%)=1600. In order to select 1600 lightnesses Y indescending order of lightness, i=63 is set at step S1, and the initialvalue of the frequency L is set to L=L(63) (step S41).

At step S42, t=1600 and L=L(63) are compared with each other, and if thefrequency L(63) is larger, the procedure proceeds to step S45, and thethreshold lightness is made Yα=63. If t=1600≧L=L(63), 1 is subtractedfrom i=63 at step S43 to make i=62, and L=L(63)+L(62) is calculated atstep S44. The procedure again returns to the step S42, t=1600 and thecalculated L are compared with each other, and if the frequency L islarger than t, the procedure proceeds to the step S45, and the thresholdlightness is made Yα=62. If t=1600≧L, L=L(63)+L(62)+L(61) . . . isrepeated to obtain Yα. In this routine, although the lightness L issequentially added like L(63)+L(62)+L(61), it is needless to say that ajudgment may be sequentially made as to, for example, whether 1600−L(63)is 0 or higher, and whether 1600−L(63)−L(62) is 0 or higher.

When the threshold lightness Yα is obtained by the procedure shown inFIG. 14, next, a control value of illumination is determined. Forexample, it is assumed that the display is a 64-gradation display, γ(gamma) correction or the like is carried out, and the characteristicsof gradation and brightness are determined. FIG. 15 shows a duty ratioselection lookup table used for selection of a duty ratio of a lightsource. In the table shown in FIG. 15, the duty ratio (%) is determinedto correspond to the value of the threshold lightness Yα obtained by theprocedure shown in FIG. 14.

Although the duty ratio may be obtained by calculation, in the casewhere a calculation expression is complicated, it is simpler to preparethe table as shown in FIG. 15. The duty ratio selection lookup table isstored in a not-shown memory in the display data conversion circuit 20.The display data conversion circuit 20 selects the specified duty ratiodata from the table on the basis of the threshold lightness Yα, andoutputs it to the light source control part 22. The light source controlpart 22 controls the light source power supply circuits 35 to 38 on thebasis of the inputted duty ratio data, and drives the cold cathodefluorescent lamps 30 to 33 at the specified duty ratio.

FIG. 16 shows a signal control value selection lookup table to determinecontrol values when the processed gradation data are outputted to theplural data bus lines 8, which are made to correspond to the thresholdlightness Yα. In the table, the uppermost row indicates the thresholdlightness Yα in descending order from the left to the right, and theleftmost column indicates the original gradation in descending order.For example, in the case where the display brightness is 360 cd at thethreshold lightness Yα=60 and 400 cd at the maximum threshold lightnessYα=63, the original gradation data is processed so that at the lightnessY=63 to 60, the light transmissivity in the liquid crystal layer becomes100%. Besides, the original gradation data is processed so that at thelightness Y≦59, the light transmissivity of the liquid crystal layerbecomes 400/360=10/9 times as high as the original light transmissivity.That is, the light transmissivity is converted to such lighttransmissivity that the display output brightness Ii of the lightness Yinot higher than the lightness Yα becomes (I÷Iα) times as high. When thecontrol values are made the table as shown in FIG. 16 and are stored ina memory, an arithmetic processing performed at all times can beomitted.

Besides, the duty ratio is determined by the lighting of alight-emitting part in accordance with the ratio of the output displaybrightness Iα of the threshold lightness Yα with respect to the maximumdisplay output brightness I(=maximum light transmissivity×maximumillumination quantity).

By combining the structure and the procedure shown in FIGS. 11 to 16,the calculation of the lightness Y and the creation of the histogram Lare performed while the gradation data (image data) of the one frame isread into a memory, and after all gradation data is read, the number Mof image display pixels is calculated, the specific value t=Mp iscalculated while the number p is made p=2%, and the threshold lightnessYα can be obtained. The duty ratio is selected by use of the table shownin FIG. 15 and is outputted to the light source control part 22, and insynchronization with this, gradation data processed in accordance withthe table shown in FIG. 16 are outputted to the respective data buslines 8.

FIG. 17 shows an example of duty driving. The horizontal directionindicates time, and the vertical direction indicates lighting (On) andnon-lighting (Off) of the light sources 30 to 33. From the left to theright, the drawing shows a duty ratio of 100% (lighting in the wholeframe), a duty ratio of 50% (lighting in the latter 50% of the frame),and a duty ratio of 20% (lighting in 20% before the last of the frame).

As a specific example, a display device was fabricated in which acircuit as described above was constructed into an FPGA, a display areawas 17 inch wide, a sidelight type backlight (fluorescent lamp wasdisposed above and below a display) or a direct type 8-lamp backlightwas used, and display brightness was a brightness of 200 to 800 nit. Amotion picture was reproduced using a commercially available DVD, thedisplay device of this embodiment and a conventional normal displaydevice were disposed side by side, and a comparison between motionpicture images was made. As a result, it was confirmed that an imagecomparable to a conventional display could be obtained also in thedisplay device of this embodiment. Besides, when the duty ratio of thebacklighting of the conventional illumination device was made 100%, itwas found that the average of the duty ratio of the display device ofthis embodiment was 50%, and an effect of power saving in the backlightcould be obtained.

Besides, when the value of p (>2%) is made further large, if the pixelsof the lightness Y exceeding the threshold lightness Yα are discrete,the influence on the picture quality is small, however, when the pixelsare concentrated, there is a case where it is judged that the picturequality is degraded. Besides, especially in the case where the pixelsare concentrated at the center of the screen, even if p is the same,there is a case where it is judged that the picture quality is degraded,and accordingly, it is needless to say that the collective/discretestate of pixels is extracted as data and may be used for preventing thepicture quality degradation. In this case, the M pixels are divided intoseveral partitions, and the numbers of elements in the respectivepartitions are made M1 to Ms, and the above procedure is used in eachthe elements of M1 to Ms.

Incidentally, a frame memory or the like did not exist in the controlcircuit 16, and even if the operation of this embodiment was appliedwith a delay of one frame ( 1/60 sec) while the image data was directlysent as the display data, in the motion picture by the commerciallyavailable DVD or the like, there did not occur a trouble that the imagewas seen to be odd or dark.

Besides, when the lightness Y was 0 to 255 (256 gradations), althoughthe illumination control values and the signal control values shouldhave been made the lookup table with respect to the threshold lightnessYα=0 to 255, the control values were simplified to 0 to 64, and therespective control values were converted into 0 when the thresholdlightness Yα=0; 1 when the threshold lightness Yα=1 to 4; 2 when thethreshold lightness Yα=5 to 8; . . . ; 64 when the threshold lightnessYα=253 to 255, and a display was carried out and the motion picture wasobserved, and as a result, an excellent result was obtained on thewhole.

FIGS. 18 to 27 show specific examples. FIG. 18 shows an example in whicha sidelight type backlight unit is disposed in an LCD panel. Coldcathode fluorescent lamps A and B are disposed at an upper part and alower part of a display area P. FIG. 19 shows an example in which thecold cathode fluorescent lamps A and B shown in FIG. 18 are duty driven.The horizontal direction indicates time, and the vertical directionindicates lighting (On) and non-lighting (Off) of the cold cathodefluorescent lamps A and B. From the left to the right in the drawing,although the duty ratio is 80% in both the cold cathode fluorescentlamps A and B in the first frame, the cold cathode fluorescent lamp A isturned on in 80% of the latter half of the frame, and the cold cathodefluorescent lamp B is turned on in 80% of the former half of the frame.In a next frame, although the duty ratio is 40% in both the cold cathodefluorescent lamps A and B, the cold cathode fluorescent lamp A is turnedon in 40% of the latter half of the frame, and the cold cathodefluorescent lamp B is turned on in 40% of the former half of the frame.

FIG. 20 shows a scan type backlight unit in which cold cathodefluorescent lamps A to F are disposed at the rear surface of a paneldisplay surface. FIG. 21 shows an example in which the cold cathodefluorescent lamps A to F are duty driven. The horizontal directionindicates time, and the vertical direction indicates lighting (On) andnon-lighting (Off) of the cold cathode fluorescent lamps A to F. Fromthe left to the right in the drawing, the duty ratio becomes 40% from80% in all of the cold cathode fluorescent lamps A to F. At this time,the lighting start points (or non-lighting points) of the cold cathodefluorescent lamps A to F are sequentially shifted by a specified time,and a scan state is formed.

FIG. 22 shows an example in which a sidelight type backlight unit isdisposed in an LCD panel. Cold cathode fluorescent lamps A and B aredisposed on the right and the left with respect to the upper center of adisplay area P, and cold cathode fluorescent lamps C and D are disposedon the right and the left with respect to the lower center of thedisplay area P. An image P1 is displayed on the left with respect to thecenter of the display area P, and an image P2 is displayed on the right.FIG. 23 shows an example in which the cold cathode fluorescent lamps Ato D shown in FIG. 22 are duty driven.

FIG. 24 shows an example in which a direct type backlight unit isdisposed in an LCD panel. Cold cathode fluorescent lamps A, C, E and Gare disposed on the left with respect to the center of a display area P,and cold cathode fluorescent lamps B, D, F and H are disposed on theright with respect to the center of the display area P. An image P1 isdisplayed on the left with respect to the center of the display area P,and an image P2 is displayed on the right. FIG. 25 shows an example inwhich the cold cathode fluorescent lamps A to H shown in FIG. 24 areduty driven.

FIG. 26 shows an example in which a direct type backlight unit isdisposed in an LCD panel. LEDs A to C, H to J, K to M and P to R aredisposed in a matrix form on the ⅔ portion of the display area P at theleft with respect to the center thereof, and LEDs D, E, I, J, N, O, Sand T are disposed in a matrix form on the ⅓ portion of the display areaP at the right with respect to the center thereof. An image P1 isdisplayed on the ⅔ portion of the display area P at the left withrespect to the center thereof, and an image P2 is displayed on the ⅓portion at the right. FIG. 27 shows an example in which the LEDs A to Tshown in FIG. 26 are duty driven.

In an arbitrary display area of the display device shown in the abovespecific examples, as the emission time of the backlight becomes short,a blur of a motion picture image intrinsic to the liquid crystal displaydevice can be improved.

In the above examples, although the average of the duty ratio of thebacklight is 50%, when an image becomes clear in total, the duty ratioapproaches 100%. When the duty ratio approaches 100%, the effect ofimproving the blur of the motion picture image becomes low. Then, asdescribed in the first and the second embodiments, two kinds of lightingstates, that is, the whole lighting state and the intermediate lightingstate are provided in one frame, and the intermediate brightness as thedisplay brightness at the time of the intermediate lighting is set to50% of the whole lighting brightness as the display brightness at thetime of the whole lighting.

For example, in the display device including the scan type backlightshown in FIG. 1 in which one frame is divided into four areas insequence from the above, and duty driving is performed in the respectiveareas, it is assumed that as shown in FIG. 28, the duty ratio is 80%,the first 20% of the one frame period is put in the non-lighting state,and the remaining 80% of the period is put in the whole lighting state.In this case, in a period between a point T2 of the first 20% (firstarea) of the one frame period and a point T3 of 25%, in spite of thefact that the gradation data is in the middle (indicated by V in thedrawing) of a writing period T1 to a pixel, the backlight is changed atthe point T2 from the non-lighting state S1 to the maximum lightingstate S2. Besides, the backlight is turned off at the time of hightransmissivity before next gradation data is written. In the one frameperiod, since the area of 20%, in total, of the four areas is in thelighting state when the gradation data is written, and are in thenon-lighting state immediately before the next gradation data iswritten, the light quantity is felt to be lower than that in theremaining area of 80%, and the display quality is degraded.

FIG. 29 shows a duty driving method for solving the above conventionalproblem. As shown in FIG. 29, in the first 40% of one frame period, thebacklight is put in the intermediate lighting state S3 (gradation datais written into a pixel in the time T1 of the first 25% of the one frameperiod). Next, the backlight is put in the maximum lighting state in theremaining 60%. By doing so, the display brightness visually sensed doesnot change, and illumination is performed by the whole lighting at thepoint when the liquid crystal almost completes the response, andtherefore, a desired image is branded on the eye. Accordingly, themotion picture blur of the image does not occur all over the displayarea and the excellent display quality is obtained.

As described above, according to this embodiment, pixels having aspecified ratio and selected in descending order of brightness in amotion image are made to have the maximum display brightness, and therespective brightnesses of the remaining pixels except for those arereproduced by lowering the duty ratio of the backlight and raising thetransmissivity of the liquid crystal. By this, even if the duty ratio ofthe backlight is lowered, it is possible to make the motion picturedisplay quality equivalent to the original image, and power saving ofthe backlight becomes possible. Besides, by the combination with a scantype backlight or a blinking type backlight, it is possible to realize ahigher quality liquid crystal display device in which the image blur isimproved while the display quality of the motion picture image is kept.Incidentally, although this embodiment is applied to the liquid crystaldisplay device, it can also be used for emission control of an EL(Electro Luminescence) element.

Fourth Embodiment

An illumination device according to a fourth embodiment of the inventionand a liquid crystal display device using the same will be describedwith reference to FIGS. 30 to 51. According to duty driving, insynchronization with a writing timing of gradation data, the brightnessof a light source of an illumination device which performs planeemission is directly modulated, however, the degree of modulation isconventionally very high, and it has been considered that the degree isrequired to make, for example, a brightness ratio of 20 or higher.However, as described in the first embodiment, even if the duty drivingin which the light source is completely turned on or off is not used,the display quality of the motion picture is not degraded. The presentinventor et al. have found that when the brightness ratio is 2 orhigher, a sufficient display can be obtained. By performing new dutydriving described below in accordance with this finding, the display canbe made to have high brightness without damaging the display quality ofthe motion picture, luminescence efficiency (electric power ratio) ofthe cold cathode fluorescent lamp can be made high, and the electricpower can be reduced. Further, the lifetime of the light source can beprolonged, and the power source can be made small, light and thin.

Example 4-1

FIG. 30 shows a backlight structure of example 1 of this embodiment. Inthis example, a TFT-LCD 1 of the first embodiment shown in FIG. 1 isused, and FIG. 30 shows a state in which an illumination device 24 isseen from the side of light emission openings of a first to a fourthlight-emitting areas. At the side of the light emission openings, adiffusion sheet 60 or the like described in the second embodiment isalso disposed. The backlight is of the direct type. Other than that,this illumination device is the similar as the illumination device 24shown in FIG. 1. FIG. 31 shows driving waveforms of the backlight of theexample 1. FIG. 31 is substantially the same as FIG. 2, and is identicalin that it shows output timings of gate pulses GP outputted to gate buslines 6 from a gate driver 12, however, there is a difference in thatFIG. 2 shows the light emission brightnesses B(25) to B(28), while FIG.31 shows currents C(30) to C(33) fed to cold cathode fluorescent lamps30 to 33 of the respective light-emitting areas 25 to 28.

As shown in FIG. 31, the currents to be fed to the respective coldcathode fluorescent lamps 30 to 33 are duty driven so that gradationdata is written into a specified pixel, the liquid crystal sufficientlyresponds and the transmissivity becomes high, and then, illumination isperformed in the maximum lighting state S2. Although the current states(or electric power states) of the respective cold cathode fluorescentlamps 30 to 33 have the maximum current (or maximum electric power) whenillumination is performed at the maximum light quantity, a current isfed (or electric power is supplied) at the other time as well, and theintermediate lighting state S3 is kept. In this duty driving, the abovecurrent state (or electric power state) is repeated at the same cycle asthe writing cycle of display data. As stated above, this example has afeature that even when the maximum current (or maximum electric power)is not fed, a current is fed (or electric power is supplied).

In the duty driving, whether a human being senses a motion picture blurof a motion picture display or a tailing phenomenon greatly depends on amaximum value of illumination light quantity in the maximum irradiationstate S2 and a time length. Even if the intermediate lighting state S3of about one half of the maximum value is made to occur between themaximum lighting states S2 repeated at a specified frequency, thequality of the motion picture display is not changed.

Thus, according to this embodiment, since the brightness can be madehigh while an increase in electric power is suppressed, it is notnecessary to enlarge a stabilizer of the cold cathode fluorescent lamp,and the stabilizer is made light and thin, and can be manufactured atlow cost. Further, since a rise in drive voltage due to an increase incurrent in the related art can also be suppressed, a drop incurrent-to-light conversion efficiency of the cold cathode fluorescentlamp is suppressed, and the tube lifetime can be made long. As statedabove, as compared with the conventional system in which illumination isperformed in the maximum lighting state S2 only for a specified time,and illumination is not performed for a time other than that, accordingto this embodiment, the quality of the motion picture display isequivalent, and it is possible to raise the brightness, to reduce theelectric power, to reduce the weight, thickness and size of the device,and to prolong the lifetime.

Example 4-2

FIG. 32 shows a backlight structure of example 2 of this embodiment. Inthis example, a TFT-LCD 1 similar to the example 1 is used, and FIG. 32shows a state viewed in the same direction as FIG. 30 of the example 1.The backlight is of the direct type. Two cold cathode fluorescent lamps(30 a, 30 b), (31 a, 31 b), (32 a, 32 b) and (33 a, 33 b) are disposedin the respective light-emitting areas 25 to 28.

FIG. 33 shows drive waveforms of the backlight of the example 2.Although the respective waveforms of FIG. 33 are substantially the sameas those of FIG. 31 of the example 1, in this example, since each of thelight-emitting areas 25 to 28 is illuminated by the pair of cold cathodefluorescent lamps, there is a merit that the respective currentwaveforms shown in FIG. 33 can be realized by the combination of the twocold cathode fluorescent lamps.

A description will be given more specifically with reference to FIGS. 34to 36. FIGS. 34 to 36 show timing charts similar to FIG. 33. In a caseshown in FIG. 34, illumination driving is performed by supplying suchcurrent to the cold cathode fluorescent lamps 30 a, 31 a, 32 a and 33 aof the respective light-emitting areas that the maximum lighting stateS2 occurs at a specified cycle, and the non-lighting state S1 occurs atthe other time. Besides, illumination driving is performed by supplyingsuch current to the cold cathode fluorescent lamps 30 b, 31 b, 32 b and33 b of the light-emitting areas that the non-lighting state S1 occursin the maximum lighting state S2 of the paired cold cathode fluorescentlamps 30 a, 31 a, 32 a and 33 a, and the intermediate lighting state S2occurs at the other time. By this, it is possible to performillumination with the brightness equal to the brightness obtained by theillumination driving current waveforms shown in FIG. 33.

In a case of FIG. 35, the cold cathode fluorescent lamps 30 a, 31 a, 32a and 33 a of the light-emitting areas are respectively driven by suchlow current that an intermediate lighting state S2′ lower than themaximum lighting state S2 occurs at a specified cycle, and at the othertime, the lamps are driven by such low current that an intermediatelighting state S3-1 lower than the intermediate lighting state S3 shownin FIG. 33 occurs. The respective cold cathode fluorescent lamps 30 b,31 b, 32 b and 33 b of the light-emitting areas are driven by such lowcurrent that a differential intermediate lighting state S3-3 occurs atthe intermediate lighting state S2′ of the respective paired coldcathode fluorescent lamps 30 a, 31 a, 32 a and 33 a so that the totalbecomes the maximum lighting state S2, and are driven by such lowcurrent that a differential intermediate lighting state S3-2 occurs atthe intermediate lighting state S3-1 of the respective cold cathodefluorescent lamps 30 a, 31 a, 32 a and 33 a so that the total becomesthe intermediate lighting state S3. By this, it is possible to performillumination with the brightness equal to the brightness obtained by theillumination driving current waveforms shown in FIG. 33.

In a case shown in FIG. 36, the cold cathode fluorescent lamps 30 a, 31a, 32 a and 33 a of the respective light-emitting areas are driven bysuch low current that an intermediate lighting state S2″ lower than themaximum lighting state S2 occurs at a specified cycle, and the currentsupply is interrupted at the other time so that the non-lighting stateS1 occurs. The cold cathode fluorescent lamps 30 b, 31 b, 32 b and 33 bof the respective light-emitting areas are continuously driven by suchlow current that a differential intermediate lighting state S3 occurs atthe intermediate lighting state S2″ of the respective paired coldcathode fluorescent lamps 30 a, 31 a, 32 a and 33 a so that the totalbecomes the maximum lighting state S2. By this, it is possible toperform illumination with the brightness equal to the brightnessobtained by the illumination driving current waveforms shown in FIG. 33.

As stated above, by controlling the current fed to the pair of the coldcathode fluorescent lamps of the respective light-emitting areas 25 to28, the illumination state shown in FIG. 33 can be obtained. Byperforming the duty driving shown in this example, the brightness can beraised while the increase in electric power is suppressed, andaccordingly, it is not necessary to enlarge the stabilizer of the coldcathode fluorescent lamp, and the stabilizer can be made light and thin,and can be manufactured at low cost. Further, since the rise in drivevoltage due to the increase in current as in the related art can also besuppressed, the drop in the current-to-light conversion efficiency ofthe cold cathode fluorescent lamp is suppressed and the tube lifetimecan be made long. As stated above, according to this embodiment, thequality of the motion picture display is the same, and it is possible toraise the brightness, to reduce the electric power, to reduce theweight, thickness and size of the device, and to prolong the lifetime.

Example 4-3

An example 3 will be described with reference to FIGS. 37 and 38. FIG.37 shows drive waveforms of backlights similarly to FIG. 31 of theexample 1. The backlight structure of this example is the same as thatof the example 1 shown in FIG. 30. In a case shown in FIG. 37, the coldcathode fluorescent lamps 30, 31, 32 and 33 of the respectivelight-emitting areas are driven by such current that the maximumlighting state S2 occurs at a specified cycle, and at the other time,they are driven by such low current (50% of the current value of themaximum lighting state S2) that the intermediate lighting state S3occurs, and further, a period in which the current supply is stopped isprovided so that when the maximum lighting state S2 is changed to theintermediate lighting state S3, the non-lighting state S1 occurs onlyfor a specified time.

In the case shown in FIG. 38, the cold cathode fluorescent lamps 30, 31,32 and 33 of the respective light-emitting areas are driven by suchcurrent that the maximum lighting state S2 occurs at a specified cycle,and at the other time, they are driven by such low current (50% of thecurrent value of the maximum lighting state S2) that the intermediatelighting state S3 occurs, and when the maximum lighting state S2 ischanged to the intermediate lighting state S3, there is provided aperiod in which low current (20% of the current value of the maximumlighting state S2) is supplied such that an intermediate lighting stateS4 clearer than the non-lighting state S1 and darker than theintermediate lighting state S3 occurs only for a specified time.

As shown in FIGS. 37 and 38, the current value (or electric power orlight quantity value) is instantaneously and largely reduced immediatelyafter the state of the maximum current value (or maximum electric poweror maximum light quantity value), so that the image is instantaneouslyvisually recognized and disappears immediately thereafter, and animpulse effect felt by a human being can be made great.

FIG. 39 shows a graph in which the current value (relative value) at themaximum lighting state S2 is made 10, the intermediate lighting statesS3 and S4 in FIG. 38 are changed, and the display quality obtained atthe time when a motion picture display is carried out on the displayarea of the TFT-LCD 1 is graphed as subjective evaluations by pluralobservers.

In FIG. 39, the horizontal axis indicates the ratio (%) of the maximumlighting state S2 to one frame period f, and the vertical axis indicatesthe evaluation according to evaluation points of from first to fifthstages. The evaluation point 1 indicates a case where a motion pictureblur, a tailing phenomenon and the like on the motion picture displayare “very obstructive”, and the evaluation point 2 indicates a casewhere those becomes “obstructive”. The evaluation point 3 indicates acase where the motion picture blur is “annoying but tolerable”, theevaluation 4 indicates a case where “a difference is seen but istolerable”, and the evaluation point 5 indicates a case where “picturequality is equivalent to a still picture and is excellent”.

In the drawing, a straight line (A) connecting circular marks indicatesa case of (current value of the maximum lighting state S2, current valueof the intermediate lighting state S4, current value of the intermediatelighting state S3)=(10, 10, 10). In this case, irrespective of the ratioof the maximum lighting state S2 to the one frame period f (hereinafterabbreviated to “ratio of the maximum lighting state S2”), illuminationis performed with the maximum brightness level in the whole area of theone frame period f. That is, the display is equivalent to the hold typedriving, and accordingly, the image quality is such that the motionpicture blur and the tailing phenomenon becomes very obstructive, andthe evaluation point becomes 1.

In the drawing, a polygonal line (B) connecting×marks indicates a caseof (current value of the maximum lighting state S2, current value of theintermediate lighting state S4, current value of the intermediatelighting state S3)=(10, 5, 5). In this case, when the ratio of themaximum lighting state S2 is in the range of from about 10% to 30%, themotion picture blur and the tailing phenomenon are hardly visuallyrecognized, and the excellent image quality is obtained, so that theevaluation point is 4. Besides, when the ratio of the maximum lightingstate S2 exceeds 30%, the evaluation is gradually lowered, however, theevaluation point 3 is obtained up to about 50%.

A polygonal line (C) indicates a case of (current value of the maximumlighting state S2, current value of the intermediate lighting state S4,current value of the intermediate lighting state S3)=(10, 2, 5). In thiscase, when the ratio of the maximum lighting state S2 is within therange of from about 10% to 30%, the motion picture blur and the tailingphenomenon are hardly visually recognized, and the excellent imagequality is obtained, so that the evaluation point is close to 5.Besides, when the ratio of the maximum lighting state S2 exceeds 30%,the evaluation is gradually lowered, however, the evaluation point 3 isobtained up to about 50%.

In the drawing, a polygonal line (D) connecting black circular marksindicates a case of (current value of the maximum lighting state S2,current value of the intermediate lighting state S4, current value ofthe intermediate lighting state S3)=(10, 0, 5). In this case, when theratio of the maximum lighting state S2 is within the range of from about10% to 30%, the motion picture blur and the tailing phenomenon arehardly visually recognized, and the excellent image quality is obtained,so that the evaluation point is close to 5. Besides, when the ratio ofthe maximum lighting state S2 exceeds 30%, the evaluation is graduallylowered, however, the evaluation point 3 or higher is obtained up toabout 50%.

In the drawing, a polygonal line (E) connecting square marks indicates acase of (current value of the maximum lighting state S2, current valueof the intermediate lighting state S4, current value of the intermediatelighting state S3)=(10, 0, 0). This is the same as the illuminationmethod of the conventional scan type LCD. In this case, when the ratioof the maximum lighting state S2 is within the range of from about 10%to 30%, the motion picture blur and the tailing phenomenon are hardlyvisually recognized, and the excellent image quality is obtained, sothat the evaluation point becomes further close to 5. Besides, when theratio of the maximum lighting state S2 exceeds 30%, the evaluation isgradually lowered, however, the evaluation point 3 or higher is obtainedup to about 50%.

From FIG. 39, it is understood that even if the intermediate lightingstate S3 is made the brightness level of about 30% of the brightnesslevel of the maximum lighting state S2, it is possible to obtain thedisplay quality comparable to the conventional scan type LCD indicatedby the polygonal line (E). Further, the brightness level of theintermediate lighting state S3 up to about 50% of the brightness levelof the maximum lighting state S2 can be regarded as being in theallowable range.

Besides, when the illumination time of the maximum lighting state S2 is30% or less of the one frame time f, the motion picture blur and thetailing phenomenon hardly occur, and the time up to 50% can be regardedas being in the allowable range.

FIG. 40 shows characteristics of a cold cathode fluorescent lamp, thehorizontal axis indicates current fed to the cold cathode fluorescentlamp, and the vertical axis indicates a duty ratio. In the drawing, twothick solid lines indicate contour lines of supplied electric power, oneof them indicates a case of an electric power of 1.0, and the otherindicate a case of an electric power of 0.6. The other nine thin solidlines indicate contour lines of brightness when the brightness from abrightness of 20 to a brightness of 100 is divided at intervals of ten.From FIG. 40, it is understood that as the value of the current fed tothe cold cathode fluorescent lamp becomes large, the current-to-lightconversion efficiency of the cold cathode fluorescent lamp is lowered,and there is a remarkable tendency that the lifetime becomes short.Besides, with respect to a stabilizer for driving the cold cathodefluorescent lamp, when the value of the current to be fed becomes large,it becomes necessary to enlarge a transformer and the like, so that thestabilizer becomes heavy, thick and expensive.

According to this embodiment, it is possible to solve the problem of thecurrent-to-light conversion efficiency of the cold cathode fluorescentlamp and the tube lifetime as shown in FIG. 40. FIGS. 41A and 41B andFIGS. 42A and 42B show effects in the case where the illumination deviceof this embodiment and the duty driving method thereof are used. Thehorizontal axis shown in FIGS. 41A and 41B and FIGS. 42A and 42Bindicates time, and the vertical axis indicate light quantity.

FIG. 41A shows conventional duty driving, and shows light quantity whenthe electric power is 1.0 (arbitrary unit: hereinafter abbreviated toa.u.) and a current of 32 mA is fed to the cold cathode fluorescent lampat a duty ratio of 33%, and shows a state in which a (time average)brightness of 1.0 (a.u.) is obtained by this. On the other hand, FIG.41B shows duty driving according to this embodiment, and shows the lightquantity when the electric power is 1.0 (a.u.), a current of 13 mA isfed in the maximum lighting state S2 to the cold cathode fluorescentlamp at a duty ratio of 33%, and a current of 5.2 mA is supplied to thecold cathode fluorescent lamp in the remainder of 67% to produce theintermediate lighting state S3. By this, a brightness of 1.4 (a.u.) isobtained.

As stated above, according to this embodiment, when the electric poweris constant, as compared with the related art, the brightness becomes1.4 times as high, and the current-to-light conversion efficiency alsobecomes 1.4 times as high. According to this embodiment, a large currentvalue may be 13 mA which is ⅖ of a conventional value. By this, forexample, when the electric power is the same, a conventional displaydevice having a display brightness of 300 candela can be made to have abrightness of 420 candela without damaging the motion picture quality.Further, the stabilizer is light, thin, short and small, and can beproduced at low cost.

FIG. 42A is the same as FIG. 41A. On the other hand, FIG. 42B indicatesduty driving according to this embodiment, and shows light quantity whenthe electric power is 1.0 (a.u.), a current of 32 mA similar to theconventional case is fed to the cold cathode fluorescent lamp in themaximum lighting state S2 at a duty ratio of 33%, and a current of 7 mAis supplied to the cold cathode fluorescent lamp in the remainder of 67%to produce the intermediate lighting state S3. According to this, theelectric power 1.5 times as large as that of the conventional system canbe supplied, and the display brightness can be doubled. That is,according to this embodiment, while the same stabilizer is used, adisplay device having a display brightness of 300 candela in theconventional system can be made to have a brightness of 600 candelawithout damaging the motion picture quality. Further, thecurrent-to-light conversion efficiency can also be improved by a factorof 1.33.

Example 4-4

An example 4 will be described with reference to FIGS. 43A and 43B. FIG.43A shows a simple section of a backlight unit 75 of this example. Theleft side of the drawing corresponds to the upper side of the displayarea of the LCD panel 2 shown in FIG. 1, and the right side of thedrawing corresponds to the lower side of the display area. For example,12 cold cathode fluorescent lamps 76 a to 761 are divided into groupseach including four lamps, and are provided in such a way that theirtube axes are substantially in parallel to the gate bus lines 6. Thecold cathode fluorescent lamps 76 a to 761 are contained in thindish-like housings, and diffuse reflection plates 77 are disposed on theinner walls of the housings. The lights from the cold cathodefluorescent lamps 76 a to 761 are emitted to a not-shown LCD panel 2 inFIG. 43A through a diffused plate 78 provided at light emissionopenings. When this structure is seen as a hold type LCD backlight unit,it is a normal structure. Since scan driving is not performed,partitions do not exist between the respective illumination areas.

In the backlight unit 75 of the structure as stated above, when thelight source is duty driven, light overflows into the surrounding areaas well, and the effect of suppressing the motion picture blur issufficiently obtained even if the partition is not provided, andfurther, when the duty driving of this embodiment is performed, theeffect of high brightness, power saving, long lifetime and the like canbe further obtained. FIG. 43B shows a relation between a frame positionand brightness at an instant in a period in which the cold cathodefluorescent lamps 76 a to 761 are scan driven at a duty ratio of 33% inthe backlight unit 75 of the structure shown in FIG. 43A so that anyfour adjacent lamps are always turned on. The left side of the drawingcorresponds to the upper side of the display area of the LCD panel 2shown in FIG. 1, and the right side of the drawing corresponds to thelower side of the display area. Although a curved line at an X positionbecomes smooth by a persistence time (8 ms) of a G (green) fluorescentsubstance in the cold cathode fluorescent lamp and the tailingphenomenon occurs, the picture quality capable of sufficientlysupporting a motion picture is obtained.

FIG. 44 shows a result obtained when the duty driving shown in FIG. 37or 38 is performed to the backlight unit 75. The horizontal axis and thevertical axis of FIG. 44 are the same as FIG. 43B. An X position of acurved line shown in FIG. 44 is steeper than that shown in FIG. 43B, andit is understood that the tailing phenomenon is more effectivelysuppressed.

More specifically, in the normal direct type backlight shown in FIGS.43A, 43B and 44, the duty driving of this embodiment is used, and acurrent supply state is not simply made to have two values (on/off) asin the related art, but is made to have the flatness in a state of asmall light quantity. Besides, the brightness distributions(illumination light quantity distributions) of FIGS. 43B and 44 arerealized by experimentally making an adjustment, as current modulationperforming smooth temporal change, in view of illumination lightquantity from the other cold cathode fluorescent lamps, and thepersistence characteristic of a fluorescent substance (when a drivecycle of a liquid crystal display device and a backlight is 60 cycle,and one frame period is 16.7 msec, the persistence time of a Gfluorescent substance is about 8 msec which can not be neglected). Theduty driving method shown in FIG. 37 or 38 is adopted, and immediatelyafter driving with a large current, in order to cancel the persistenceof the fluorescent substance, the current is greatly lowered, and then,the current is smoothly increased.

According to this example, the conventional normal direct type backlightstructure is used as it is, and the scan driving without degradation ofthe motion picture quality can be performed, and further, lightquantities of many lamps can be mixed, and accordingly, even ifrelatively large color irregularity and brightness irregularity exist inthe cold cathode fluorescent lamps, those are made uniform and can bemade not to be visually recognized. Further, since it is also possibleto make color irregularity and brightness irregularity due todegradation unable to be visually recognized, the lifetime of thedisplay device can be made long.

As a comparative example, FIGS. 45A and 45B and FIG. 46 show aconventional direct type backlight unit structure and duty driving. In abacklight 74 shown in FIG. 45A, partitions 77 are respectively disposedbetween respective cold cathode fluorescent lamps 76 a to 76 l. Then, atthe time of the duty driving, as shown in FIG. 45B, current issequentially supplied to the cold cathode fluorescent lamps 76 a to 76 land they are individually turned on/off one by one. FIG. 46 shows aresult obtained when the conventional duty driving is performed to thebacklight unit 74. The horizontal axis and the vertical axis of FIG. 46are the same as FIG. 43B. From FIG. 46, it is understood that the motionpicture blur and the tailing phenomenon do not occur, however, it isunderstood that since only a part (in the drawing, positions 114 to 140and their vicinities) is in a lighting state in the whole frameposition, a desired brightness is not obtained.

Example 4-5

FIG. 47 shows a backlight unit 75′ of example 5. This example shows thebacklight unit 75′ which includes the backlight unit 75 shown in FIG.43A or the conventional backlight unit having incomplete partitionsformed between the respective light-emitting areas and in which asidelight type backlight unit is disposed above a diffused plate 78 of alight emission opening. In the sidelight type backlight unit, coldcathode fluorescent lamps 79 which are always turned on and are foruniform illumination are disposed at both ends of a prism light guideplate 80. Also by this structure, the same effect as the example 3 canbe obtained.

Example 4-6

FIG. 48 shows a backlight unit 130 of example 6. The backlight unit 130of this example includes two light guide plates 100 and 100′ which arelaminated and disposed. The light guide plates 100 and 100′ include fourlight-emitting areas B1, B2, A1 and A2. A cold cathode fluorescent lamp102 a is disposed at one side end face of the lower light guide plate100 in the drawing. Besides, a cold cathode fluorescent lamp 102 b isdisposed at the other side end face of the light guide plate 100. Thelight guide plate 100 includes a light guide area for guiding light fromthe cold cathode fluorescent lamps 102 a and 102 b. In the light guideplate 100 of the light-emitting area B1, an opposite surface 114 isinclined with respect to a light emission surface 112 so that thethickness at the side of the cold cathode fluorescent lamp 102 a is thinand the thickness at the side of the cold cathode fluorescent lamp 102 bis thick, and is formed into a wedge shape. Besides, in the light guideplate 100 of the light-emitting area A1, an opposite surface 114 isinclined with respect to the light emission surface 112 so that thethickness at the side of the cold cathode fluorescent lamp 102 a isthick, and the thickness at the side of the cold cathode fluorescentlamp 102 b is thin, and is formed into a wedge shape. Scattering layers116 as light scattering elements are formed on the opposite surfaces 114of the light-emitting areas A1 and B1. The light guide plate 100includes the light guide area for guiding the light from the coldcathode fluorescent lamps 102 a and 102 b.

A cold cathode fluorescent lamp 102 a′ is disposed at one side end faceof the light guide plate 100′ laminated and disposed at the liquidcrystal display panel 2 side of the light guide plate 100. Besides, acold cathode fluorescent lamp 102 b′ is disposed at the other side endface of the light guide plate 100′. The light guide plate 100′ includesa light guide area for guiding light from the cold cathode fluorescentlamps 102 a′ and 102 b′. In the light guide plate 100′ of thelight-emitting area B2, an opposite surface 114 is inclined with respectto a light emission surface 112 so that the thickness at the side of thecold cathode fluorescent lamp 102 a′ is thin, and the thickness at theside of the cold cathode fluorescent lamp 102 b′ is thick, and is formedinto a wedge shape. Besides, in the light guide plate 100′ of thelight-emitting area A2, an opposite surface 114 is inclined with respectto the light emission surface 112 so that the thickness at the side ofthe cold cathode fluorescent lamp 102 a′ is thick, and the thickness atthe side of the cold cathode fluorescent lamp 102 b′ is thin, and isformed into a wedge shape. Scattering layers 116 as light scatteringelements are formed on the opposite surfaces 116 of the areas A2 and B2.

In the light-emitting area B1 of the light guide plate 100, the lightguided from the side of the cold cathode fluorescent lamp 102 b isscattered by the scattering layer 116 when it is reflected at theopposite surface 114, and the incident angle with respect to the lightemission surface 112 becomes small by the wedge shape of the light guideplate 100 each time it is reflected at the opposite surface 114. Thus,most of the light guided from the side of the cold cathode fluorescentlamp 102 b is not kept being guided in the light-emitting area B1, andis emitted to the outside of the light guide plate 100. On the otherhand, although light guided from the side of the cold cathodefluorescent lamp 102 a to the light-emitting area B1 is scattered by thescattering layer 116 when it is reflected at the opposite surface, thelight is concentrated by the wedge shape of the light guide plate 100each time it is reflected, and the incident angle with respect to thelight emission surface 112 becomes large. Thus, the light guided fromthe side of the cold cathode fluorescent lamp 102 a to thelight-emitting area B1 is kept being guided in the light-emitting areaB1, and is not emitted to the outside of the light guide plate 100 much.That is, the light-emitting area B1 of the light guide plate 100 has arelation of (extracted light quantity from the side of the cold cathodefluorescent lamp 102 b/guided light quantity from the side of the coldcathode fluorescent lamp 102 b)>(extracted light quantity from the sideof the cold cathode fluorescent lamp 102 a/guided light quantity fromthe side of the cold cathode fluorescent lamp 102 a).

In the light-emitting area A1 of the light guide plate 100, light guidedfrom the side of the cold cathode fluorescent lamp 102 a is scattered bythe scattering layer 116 when it is reflected at the opposite surface114, and the incident angle with respect to the light emission surface112 becomes small by the wedge shape of the light guide plate 100 eachtime it is reflected at the opposite surface 114. Thus, most of thelight guided from the side of the cold cathode fluorescent lamp 102 isnot kept being guided in the light-emitting area A1, and is emitted tothe outside of the light guide plate 100. On the other hand, althoughlight guided from the side of the cold cathode fluorescent lamp 102 b tothe light-emitting area A1 is scattered by the scattering layer 116 whenit is reflected at the opposite surface 114, the light is concentratedby the wedge shape of the light guide plate 100 each time it isreflected, and the incident angle with respect to the light emissionsurface 112 becomes large. Thus, the light guided from the side of thecold cathode fluorescent lamp 102 b to the light-emitting area A1 iskept being guided in the light-emitting area A1, and is not emitted tothe outside of the light guide plate 100 much. That is, thelight-emitting area A1 of the light guide plate 100 has a relation of(extracted light quantity from the side of the cold cathode fluorescentlamp 102 a/guided light quantity from the side of the cold cathodefluorescent lamp 102 a)>(extracted light quantity from the side of thecold cathode fluorescent lamp 102 b/guided light quantity from the sideof the cold cathode fluorescent lamp 102 b).

In the light-emitting area B2 of the light guide plate 100′, lightguided from the side of the cold cathode fluorescent lamp 102 b′ isscattered by the scattering layer 116 when it is reflected at theopposite surface 114, and the incident angle with respect to the lightemission surface 112 becomes small by the wedge shape of the light guideplate 100 each time it is reflected at the opposite surface 114. Thus,most of the light guided from the side of the cold cathode fluorescentlamp 102 b′ is not kept being guided in the light-emitting area B2, andis emitted to the outside of the light guide plate 100. On the otherhand, although light guided from the side of the cold cathodefluorescent lamp 102 a′ to the light-emitting area B2 is scattered bythe scattering layer 116 when it is reflected at the opposite surface114, the light is concentrated by the wedge shape of the light guideplate 100 each time it is reflected, and the incident angle with respectto the light emission surface 112 becomes large. Thus, the light guidedfrom the side of the cold cathode fluorescent lamp 102 a′ to thelight-emitting area B2 is kept being guided in the light-emitting areaB2, and is not emitted to the outside of the light guide plate 100 much.That is, the light-emitting area B2 of the light guide plate 100′ has arelation of (extracted light quantity from the side of the cold cathodefluorescent lamp 102 b′/guided light quantity from the side of the coldcathode fluorescent lamp 102 b′)>(extracted light quantity from the sideof the cold cathode fluorescent lamp 102 a′/guided light quantity fromthe side of the cold cathode fluorescent lamp 102 a′).

In the light-emitting area A2 of the light guide plate 100′, lightguided from the side of the cold cathode fluorescent lamp 102 a′ isscattered by the scattering layer 116 when it is reflected at theopposite surface 114, and the incident angle with respect to the lightemission surface 112 becomes small by the wedge shape of the light guideplate 100 each time it is reflected at the opposite surface 114. Thus,most of the light guided from the side of the cold cathode fluorescentlamp 102 a′ is not kept being guided in the light-emitting area A2, andis emitted to the outside of the light guide plate 100. On the otherhand, although light guided from the side of the cold cathodefluorescent lamp 102 b′ to the light-emitting area A2 is scattered bythe scattering layer 116 when it is reflected at the opposite surface114, the light is concentrated by the wedge shape of the light guideplate 100 each time it is reflected, and the incident angle with respectto the light emission surface 112 becomes large. Thus, the light guidedfrom the side of the cold cathode fluorescent lamp 102 b′ to thelight-emitting area A2 is kept being guided in the light-emitting areaA2, and is not emitted to the outside of the light guide plate 100 much.That is, the light-emitting area B2 of the light guide plate 100′ has arelation of (extracted light quantity from the side of the cold cathodefluorescent lamp 102 a′/guided light quantity from the side of the coldcathode fluorescent lamp 102 a′)>(extracted light quantity from the sideof the cold cathode fluorescent lamp 102 b′/guided light quantity fromthe side of the cold cathode fluorescent lamp 102 b′).

The light-emitting areas B2 and A2 of the light guide plate 100 arenon-light-extraction areas in which both the light from the cold cathodefluorescent lamp 102 a and the light from the cold cathode fluorescentlamp 102 b are hardly extracted. Besides, the light-emitting areas B1and A1 of the light guide plate 100′ are non-light-extraction areas inwhich both the light from the cold cathode fluorescent lamp 102 a′ andthe light from the cold cathode fluorescent lamp 102 b′ are hardlyextracted.

As stated above, in the light-emitting area A1 of the light guide plate100, the light guided from the side of the cold cathode fluorescent lamp102 a is more extracted, and in the light-emitting area B1, the lightguided from the side of the cold cathode fluorescent lamp 102 b is moreextracted. In the light-emitting area A2 of the light guide plate 100′,the light guided from the side of the cold cathode fluorescent lamp 102a is more extracted, and in the light-emitting area B2, the light guidedfrom the side of the cold cathode fluorescent lamp 102 b′ is moreextracted. Besides, when the light guide plates 100 and 100′ arelaminated and disposed, the light is almost uniformly extracted in allthe light-emitting areas B1, A1, B2 and A2.

A sidelight type backlight unit is further disposed on theabove-described backlight unit. In the sidelight type backlight unit,cold cathode fluorescent lamps 79 which are always turned on and are foruniform illumination, are disposed at both ends of a prism light guideplate 80. Also in this structure, the same effect as the example 3 canbe obtained.

Example 4-7

FIG. 49 shows a backlight structure of example 7 of this embodiment.This example also uses the TFT-LCD 1 according to the first embodimentshown in FIG. 1, and FIG. 49 shows a state in which a sidelight typebacklight unit 82 is viewed from the side of light emission openings offirst to fourth light-emitting areas 25 to 28. In the sidelight typebacklight unit 82, LEDs (Light-Emitting Diode) (84 a, 84 b), (85 a, 85b), (86 a, 86 b) and (87 a, 87 b) are disposed at both sides of lightguide plates 83 for the respective light-emitting areas 25 to 28. It isthe similar as the illumination device 24 shown in FIG. 1. Also when theduty driving of this embodiment is applied to the backlight unit of thestructure shown in FIG. 49, the effect equivalent to the above examplecan be obtained.

FIG. 50 shows current dependency of light emission efficiency of an LED.The horizontal axis indicates current supplied to the LED, and thevertical axis indicates light emission efficiency (a.u.). FIG. 51 showscurrent dependency of light emission quantity of an LED. The horizontalaxis indicates current supplied to the LED, and the vertical axisindicates light emission quantity (a.u.). In both the drawings, a curvedline connecting rhombic marks indicates a characteristic of an LED of Gaquaternary system (for red), a curved line connecting black circularmarks indicates a characteristic of an LED of GaN system 1 (for blue),and a curved line connecting white circular marks indicates acharacteristic of an LED of GaN system 2 (for green).

As shown in FIGS. 50 and 51, it is understood that in the GaN system LEDof green (G) light emission and blue (B) light emission, thecurrent-to-light conversion efficiency is lowered by an increase incurrent similarly to the cold cathode fluorescent lamp. In addition,with respect to current, duty ratio, electric power, current-to-lightconversion efficiency, light emission quantity and lifetime, the LED hassimilar characteristics to the cold cathode fluorescent lamp.Accordingly, almost all particulars explained on the cold cathodefluorescent lamp as an example in the above embodiment can be applied tothe LED as well. Further, since another discharge lamp or solid lightemission element also has a tendency to have almost similarcharacteristics, the above embodiment can be applied to almost all lightsources.

As described above, according to this embodiment, it is possible torealize the display device which has high brightness, has highcurrent-to-light conversion efficiency, has low cost, is light, thin,short and small, has long lifetime, is superior in uniformity of colorand brightness, and is excellent in motion picture quality.

Fifth Embodiment

An illumination device according to a fifth embodiment of the inventionand a liquid crystal display device using the same will be describedwith reference to FIGS. 52 to 68. First, a basic structure of theillumination device according to this embodiment will be described withreference to FIGS. 52 to 56. FIG. 52 shows the basic structure of theillumination device according to this embodiment. As shown in FIG. 52,the illumination device of this basic structure includes a light guideplate 100 having substantially a plate shape and made of, for example,acryl. A linear light source, for example, a cold cathode fluorescentlamp 102 b is disposed at the upper side end face of the light guideplate 100 in the drawing while the tube axial direction is substantiallyparallel to the long side direction of the light guide plate 100.Besides, a cold cathode fluorescent lamp 102 a is disposed at the lowerend face of the light guide plate 100 in the drawing while for example,the tube axial direction is substantially parallel to the long sidedirection of the light guide plate 100. The light guide plate 100includes a light emission surface 112 for emitting light, and anopposite surface 114 opposite to the light emission surface 112.Besides, the light guide plate 100 includes four light-emitting areasA1, B1, A2 and B2 divided substantially parallel to the tube axialdirection of the cold cathode fluorescent lamps 102 a and 102 b. Thelight-emitting areas A1, B1, A2 and B2 of the light guide plate 100 areintegrally formed, and a slit is not formed at boundaries of therespective light-emitting areas A1, B1, A2 and B2.

The light-emitting areas A1 and A2 include light extraction elements formainly extracting light guided from the side of the cold cathodefluorescent lamp 102 a (or the cold cathode fluorescent lamp 102 b) tothe outside of the light guide plate 110. The light-emitting areas B1and B2 include light extraction elements for mainly extracting lightguided from the side of the cold cathode fluorescent lamp 102 b (or thecold cathode fluorescent lamp 102 a) to the outside of the light guideplate 110. The light-emitting areas A1 and A2 (or B1 and B2) forselectively extracting light guided from the one cold cathodefluorescent lamp 102 a (or 102 b) are arranged alternately with thelight-emitting areas B1 and B2 (or A1 and A2) for selectively extractinglight guided from the other cold cathode fluorescent lamp 102 b (or 102a). By this, the light-emitting areas A1 and A2 (B1 and B2) forselectively extracting the light guided from the same cold cathodefluorescent lamp 102 a or 102 b are not adjacent to each other.

The illumination device according to this basic structure is of thesidelight type that uses the linear light source. Thus, excellentdisplay quality without uneven brightness can be obtained. Besides, inthe illumination device according to this basic structure, even if thelight-emitting area is divided in parallel to the long side direction ofthe light guide plate 100, the tube axial direction of the cold cathodefluorescent lamps 102 a and 102 b can be disposed to be substantiallyparallel to the long side direction of the light guide plate 100. Thus,the linear light source having relatively large light emission quantityand long length can be used, and high brightness can be obtained.

FIG. 53 is a view for explaining a first principle of a light extractionelement of the illumination device according to this basic structure. Asshown in FIG. 53, a cold cathode fluorescent lamp 102 a is disposed atone side end face (left end face in FIG. 53) of a light guide plate 100while for example, the tube axial direction is substantially parallel tothe long side direction of the light guide plate 100. Besides, a coldcathode fluorescent lamp 102 b is disposed at the other side end face(right end face in FIG. 53) of the light guide plate 100 while the tubeaxial direction is substantially parallel to the long side direction ofthe light guide plate 100. Lamp reflectors 110 are disposed around thecold cathode fluorescent lamps 102 a and 102 b. The light guide plate100 includes a light emission surface 112 for emitting light, and anopposite surface 114 opposite to the light emission surface 112. Ascattering layer 116 as a light scattering element for scattering andreflecting light is formed on the surface of the opposite surface 114.The scattering layer 116 is made of, for example, resin in which beadsor the like are mixed, and is formed to have a specified area andgradation. Besides, the light guide plate 100 includes twolight-emitting areas A and B divided substantially in parallel to thetube axial direction of the cold cathode fluorescent lamps 102 a and 102b. The light-emitting area B is disposed at the side of the cold cathodefluorescent lamp 102 a, and the light-emitting area A is disposed at theside of the cold cathode fluorescent lamp 102 b. The light-emittingareas A and B of the light guide plate 100 are integrally formed, and aslit is not formed at the boundary of the respective light-emittingareas A and B. The light guide plate 100 includes a light guide area forguiding the lights from the cold cathode fluorescent lamps 102 a and 102b.

The light guide plate 100 of the light-emitting area A is formed intosuch a wedge shape that the thickness at a side end where the coldcathode fluorescent lamp 102 b is disposed is thin, and the thickness atthe center is thick. The light guide plate 100 of the light-emittingarea B is formed into such a wedge shape that the thickness at the otherside end where the cold cathode fluorescent lamp 102 a is disposed isthin, and the thickness at the center is thick. The wedge shape of thelight guide plate 100, together with the light scattering element,functions as the light extraction element.

In the light-emitting area B, light guided through the light guide plate100 from the side of the cold cathode fluorescent lamp 102 a isscattered by the scattering layer 116 when it is reflected at theopposite surface 114. However, the light is concentrated by the wedgeshape of the light guide plate 100 each time it is reflected, and theincident angle with respect to the light emission surface 112 becomeslarge. Thus, the light guided from the side of the cold cathodefluorescent lamp 102 a is kept being guided in the light-emitting area Blike a light beam L1, and is not emitted to the outside of the lightguide plate 100 much. On the other hand, light guided from the side ofthe cold cathode fluorescent lamp 102 b is scattered by the scatteringlayer 116 when it is reflected at the opposite surface 114, and theincident angle with respect to the light emission surface 112 becomessmall by the wedge shape of the light guide plate 100 each time it isreflected at the opposite surface 114. Thus, the light guided from theside of the cold cathode fluorescent lamp 102 b is not kept being guidedin the light-emitting area B, and is emitted to the outside of the lightguide plate 100 like a light beam L4. That is, the light-emitting area Bhas a relation of (extracted light quantity from the side of the coldcathode fluorescent lamp 102 b/guided light quantity from the side ofthe cold cathode fluorescent lamp 102 b)>(extracted light quantity fromthe side of the cold cathode fluorescent lamp 102 a/guided lightquantity from the side of the cold cathode fluorescent lamp 102 a).

In the light-emitting area A, light guided through the light guide plate100 from the side of the cold cathode fluorescent lamp 102 b isscattered by the scattering layer 116 when it is reflected at theopposite surface 114. However, the light is concentrated by the wedgeshape of the light guide plate 100 each time it is reflected, and theincident angle with respect to the light emission surface 112 becomeslarge. Thus, the light guided from the side of the cold cathodefluorescent lamp 102 b is kept being guided in the light-emitting area Alike a light beam L3, and is not emitted to the outside of the lightguide plate 100 much. On the other hand, light guided from the side ofthe cold cathode fluorescent lamp 102 a is scattered by the scatteringlayer 116 when it is reflected at the opposite surface 114, and theincident angle with respect to the light emission surface 112 becomessmall by the wedge shape of the light guide plate 100 each time it isreflected at the opposite surface 114. Thus, the light guided from theside of the cold cathode fluorescent lamp 102 a is not kept being guidedin the light-emitting area A, and is emitted to the outside of the lightguide plate 100 like a light beam L2. That is, the light-emitting area Ahas a relation of (extracted light quantity from the side of the coldcathode fluorescent lamp 102 a/guided light quantity from the side ofthe cold cathode fluorescent lamp 102 a)>(extracted light quantity fromthe side of the cold cathode fluorescent lamp 102 b/guided lightquantity from the side of the cold cathode fluorescent lamp 102 b).

As stated above, in the light-emitting area A of the light guide plate100, the light guided from the side of the cold cathode fluorescent lamp102 a is more extracted, and in the light-emitting area B, the lightguided from the side of the cold cathode fluorescent lamp 102 b is moreextracted. Incidentally, it is appropriate that the interface of thescattering layer 116 at the air side is formed to be flat (so-calledbulk type scatter structure) rather than formed to be uneven. By this,it is possible to greatly reduce the ratio at which the light from theside of the cold cathode fluorescent lamp 102 a (the side of the coldcathode fluorescent lamp 102 b) is emitted from the interface of thescattering layer 116 of the light-emitting area B (light-emitting areaA) to the side of the air layer.

FIG. 54 is a view for explaining a second principle of a lightextraction element of the illumination device according to this basicstructure. As shown in FIG. 54, a light guide plate 100 includes twolight-emitting areas A and B divided substantially in parallel to thetube axial direction of cold cathode fluorescent lamps 102 a and 102 b.The light-emitting area B is disposed at the side of the cold cathodefluorescent lamp 102 a, and the light-emitting area A is disposed at theside of the cold cathode fluorescent lamp 102 b. The light-emittingareas A and B of the light guide plate 100 are integrally formed, and aslit is not formed at the boundary of the respective light-emittingareas A and B. An opposite surface 114 of the light guide plate 100 isformed into a prism shape. The prism shape functions as the lightextraction element for extracting light.

The opposite surface 114 of the light-emitting area B has such a prismshape that light from the side of the cold cathode fluorescent lamp 102a is not incident on a prism surface 118, but is guided to thelight-emitting area A as it is like a light beam L1. The prism surface118 is formed to have an inclination angle of, for example, 40° to 45°with respect to a light emission surface 112. On the other hand, lightfrom the side of the cold cathode fluorescent lamp 102 b is incident onthe prism surface 118 at a certain probability. The light incident onthe prism surface comes not to satisfy a total reflection condition andis emitted to the outside of the light guide plate 100 like a light beamL4 by reflection or refraction.

The opposite surface 114 of the light-emitting area A has such a prismshape that light from the side of the cold cathode fluorescent lamp 102b is not incident on a prism surface 119, but is guided to thelight-emitting area B as it is like a light beam L3. The prism surface119 is formed to have an inclination angle of, for example, 40° to 45°with respect to the light emission surface 112. On the other hand, lightfrom the side of the cold cathode fluorescent lamp 102 a is incident onthe prism surface 119 at a certain probability. The light incident onthe prism surface 119 comes not to satisfy the total reflectioncondition and is emitted to the outside of the light guide plate 100like a light beam L2 by reflection or refraction.

As stated above, in the light-emitting area A of the light guide plate100, the light guided from the side of the cold cathode fluorescent lamp102 a is more extracted, and in the light-emitting area B, the lightguided from the side of the cold cathode fluorescent lamp 102 b is moreextracted.

FIG. 55 is a view for explaining a third principle of a light extractionelement of the illumination device according to this basic structure. Asshown in FIG. 55, a scattering layer 116 as a light scattering elementfor scattering and reflecting light is formed on the surface of anopposite surface 114 of a light guide plate 100. The light guide plate100 includes two light-emitting areas A and B divided substantially inparallel to the tube axial direction of cold cathode fluorescent lamps102 a and 102 b. The light-emitting area A is disposed at the side ofthe cold cathode fluorescent lamp 102 a, and the light-emitting area Bis disposed at the side of the cold cathode fluorescent lamp 102 b.

The light guide plate 100 of the light-emitting area A is formed intosuch a wedge shape that the thickness at the side of a side end wherethe cold cathode fluorescent lamp 102 a is disposed is thick, and thethickness at the center is thin. Similarly, the light guide plate 100 ofthe light-emitting area B is formed into such a wedge shape that thethickness at the side of a side end where the cold cathode fluorescentlamp 102 b is disposed is thick, and the thickness at the center isthin. The light-emitting areas A and B of the light guide plate 100 areintegrally formed and a slit is not formed at the boundary of therespective light-emitting areas A and B. Besides, the light-emittingareas A and B are not completely separated. The wedge shape of the lightguide plate 100, together with the light scattering element, functionsas the light extraction element.

In the light-emitting area A, light guided from the side of the coldcathode fluorescent lamp 102 a is scattered by the scattering layer 116when it is reflected at the opposite surface 114, and the incident anglewith respect to a light emission surface 112 becomes small by the wedgeshape of the light guide plate 100 each time it is reflected at theopposite surface 114. Thus, most of the light guided from the side ofthe cold cathode fluorescent lamp 102 a is not kept being guided in thelight-emitting area A and is emitted to the outside of the light guideplate 100. On the other hand, although the light guided to thelight-emitting area B from the side of the cold cathode fluorescent lamp102 a is scattered by the scattering layer 116 when it is reflected atthe opposite surface 114, the light is concentrated by the wedge shapeof the light guide plate 100 each time it is reflected, and the incidentangle with respect to the light emission surface 112 becomes large.Thus, the light guided to the light-emitting area B from the side of thecold cathode fluorescent lamp 102 a is kept being guided in thelight-emitting area B, and is not emitted to the outside of the lightguide plate 100 much.

In the light-emitting area B, light guided from the side of the coldcathode fluorescent lamp 102 b is scattered by the scattering layer 116when it is reflected at the opposite surface 114, and the incident anglewith respect to the light emission surface 112 becomes small by thewedge shape of the light guide plate 100 each time it is reflected atthe opposite surface 114. Thus, most of the light guided from the sideof the cold cathode fluorescent lamp 102 b is not kept being guided inthe light-emitting area B and is emitted to the outside of the lightguide plate 100. On the other hand, although the light guided to thelight-emitting area A from the side of the cold cathode fluorescent lamp102 b is scattered by the scattering layer 116 when it is reflected atthe opposite surface 114, the light is concentrated by the wedge shapeof the light guide plate 100, and the incident angle with respect to thelight emission surface 112 becomes large. Thus, the light guided to thelight-emitting area A from the side of the cold cathode fluorescent lamp102 b is kept being guided in the light-emitting area A, and is notemitted to the outside of the light guide plate 100 much.

As stated above, in the light-emitting area A of the light guide plate100, the light guided from the side of the cold cathode fluorescent lamp102 a is more extracted, and in the light-emitting area B, the lightguided from the side of the cold cathode fluorescent lamp 102 b is moreextracted.

FIG. 56 is a view for explaining a fourth principle of a lightextraction element of the illumination device according to this basicstructure. As shown in FIG. 56, a light guide plate 100 includes twolight-emitting areas A and B divided substantially in parallel to thetube axial direction of cold cathode fluorescent lamps 102 a and 102 b.The light-emitting area A is disposed at the side of the cold cathodefluorescent lamp 102 a, and the light-emitting area B is disposed at theside of the cold cathode fluorescent lamp 102 b. An opposite surface 114of the light guide plate 100 is formed into a prism shape. The prismshape functions as a light extraction element for extracting light. Thelight-emitting areas A and B of the light guide plate 100 are integrallyformed, and a slit is not formed at the boundary of the respectivelight-emitting areas A and B.

The opposite surface 114 of the light-emitting area A has such a prismshape that light from the side of the cold cathode fluorescent lamp 102a is incident on a prism surface 119 at a certain probability, and lightfrom the side of the cold cathode fluorescent lamp 102 b is not incidenton the prism surface 119. The prism surface 119 is formed to have aninclination angle of, for example, 40° to 45° with respect to the lightemission surface 112. The light incident on the prism surface 119 comesnot to satisfy the total reflection condition and is emitted to theoutside of the light guide plate 100 by reflection or refraction.

The opposite surface 114 of the light-emitting area B has such a prismshape that light from the side of the cold cathode fluorescent lamp 102b is incident on a prism surface 118 at a certain probability, and lightfrom the side of the cold cathode fluorescent lamp 102 a is not incidenton the prism surface 118. The prism surface 118 is formed to have aninclination angle of, for example, 40° to 45° with respect to the lightemission surface 112. The light incident on the prism surface 118 comesnot to satisfy the total reflection condition and is emitted to theoutside of the light guide plate 100 by reflection or refraction.

As stated above, in the light-emitting area A of the light guide plate100, the light guided from the side of the cold cathode fluorescent lamp102 a is more extracted, and in the light-emitting area B, the lightguided from the side of the cold cathode fluorescent lamp 102 b is moreextracted.

Hereinafter, an illumination device according to this embodiment and aliquid crystal display device using the same will be describedspecifically with reference to examples 5-1 to 5-6.

Example 5-1

An illumination device according to example 5-1 of this embodiment and aliquid crystal display device using the same will be described withreference to FIGS. 57 to 61. FIG. 57 is a block diagram showing a roughstructure of the liquid crystal display device according to thisexample. As shown in FIG. 57, the liquid crystal display device includesa backlight unit 130, a control circuit 16, and a driving circuitcomposed of a gate driver 12 and a data driver 14. The backlight unit130 includes a light source control part (light source driving circuit)132. The light source control part 132 is connected to the controlcircuit 16. A clock CLK outputted from a system side such as a PC, adata enable signal Enab, gradation data Data and the like are inputtedto the control circuit 16. Besides, the control circuit 16 includes aframe memory (not shown) for storing image signals of one frame. Thegate driver 12 and the data driver 14 are connected to the controlcircuit 16. The gate driver 12 includes, for example, a shift register,receives a latch pulse signal LP from a gate driver control part in thecontrol circuit 16, and sequentially outputs a gate pulse to linesstarting from a display start line to perform line sequential driving.

The liquid crystal display device includes N gate bus lines 6-1 to 6-N(only four lines are shown in FIG. 57) in a display area 134. Therespective gate bus lines 6-1 to 6-N are connected to the gate driver12. The display area 134 is divided into four areas B1, A1, B2 and A2extending in parallel to the gate bus line 6. The areas B1, A1, B2 andA2 are respectively illuminated by the corresponding light-emittingareas B1, A1, B2 and A2 of the backlight unit 130. The gate bus lines6-1 to 6-(N/4) are disposed in the area B1. The gate bus lines 6-(N/4+1)to 6-(N/2) are disposed in the area A1. The gate bus lines 6-(N/2+1) to6-(3×N/4) are disposed in the area B2. The gate bus lines 6-(3×N/4+1) to6-N are disposed in the area A2.

FIG. 58 shows a sectional structure of the liquid crystal display deviceaccording to this example. FIG. 59 shows a sectional structure of thebacklight unit 130 of the illumination device according to this example.As shown in FIGS. 58 and 59, the liquid crystal display device includesa transmission type LCD panel 2 and the backlight unit 130. Thebacklight unit 130 includes a substantially plate-shaped light guideplate 100.

A cold cathode fluorescent lamp 102 a of a linear light source isdisposed at one end face (left end face in FIGS. 58 and 59) of the lightguide plate 100 while for example, the tube axial direction issubstantially parallel to the long side direction of the light guideplate 100. Besides, a cold cathode fluorescent lamp 102 b is disposed atthe other end face (right end face in FIGS. 58 and 59) of the lightguide plate 100 while for example, the tube axial direction issubstantially parallel to the long side direction of the light guideplate 100. Lamp reflectors 110 are disposed around the cold cathodefluorescent lamps 102 a and 102 b. The light guide plate 100 includes alight emission surface 112 for emitting light and an opposite surface114 opposite to the light emission surface 112. A scattering layer 116as a light scattering element is formed on the opposite surface 114.Besides, the light guide plate 100 includes four light-emitting areasB1, A1, B2 and A2 divided substantially in parallel to the tube axialdirection of the cold cathode fluorescent lamps 102 a and 102 b. Thelight-emitting area B1 is disposed at the side of the cold cathodefluorescent lamp 102 a, and the light-emitting area A1 is disposed to beadjacent to the light-emitting area B1. The light-emitting area B2 isdisposed to be adjacent to the light-emitting area A1, and thelight-emitting area A2 is disposed at the side of the cold cathodefluorescent lamp 102 b. The light-emitting areas B1, A1, B2 and A2 areintegrally formed, and a slit is not formed at boundaries of therespective light-emitting areas B1, A1, B2 and A2.

The opposite surface 114 of the light-emitting areas B1 and B2 has sucha prism shape that light from the side of the cold cathode fluorescentlamp 102 a is not incident on a prism surface 118, but is guided to theside of the cold cathode fluorescent lamp 102 b as it is. The prismsurface 118 is formed to have an inclination angle of, for example, 40°to 45° with respect to the light emission surface 112. On the otherhand, light from the side of the cold cathode fluorescent lamp 102 b isincident on the prism surface 118 at a certain probability. The lightincident on the prism surface 118 comes not to satisfy the totalreflection condition and is emitted to the outside of the light guideplate 100 by reflection or refraction.

The opposite surface 114 of the light-emitting areas A1 and A2 has sucha prism shape that light from the side of the cold cathode fluorescentlamp 102 b is not incident on a prism surface 119, but is guided to theside of the cold cathode fluorescent lamp 102 b as it is. The prismsurface 119 is formed to have an inclination angle of, for example, 40°to 45° with respect to the light emission surface 112. On the otherhand, light from the side of the cold cathode fluorescent lamp 102 a isincident on the prism surface 119 at a certain probability. The lightincident on the prism surface 119 comes not to satisfy the totalreflection condition and is emitted to the outside of the light guideplate 100 by reflection or refraction.

As stated above, in the light-emitting areas A1 and A2 of the lightguide plate 100, the light guided from the side of the cold cathodefluorescent lamp 102 a is more extracted, and in the light-emittingareas B1 and B2, the light guided from the side of the cold cathodefluorescent lamp 102 b is more extracted. Besides, in the light guideplate 100, light can be extract almost uniformly in all thelight-emitting areas B1, A1, B2 and A2.

A light distribution sheet group 136 including plural light distributionsheets, for improving a light distribution characteristic is disposedbetween the LCD panel 2 and the light guide plate 100. Besides, areflection scattering sheet 138 for scattering and reflecting light isdisposed at the side of the opposite surface 114 of the light guideplate 100.

FIG. 60 shows a driving method of the illumination device according tothis example and the liquid crystal display device using the same. Thehorizontal axis direction indicates time, and the vertical axisdirection indicates a writing state (writing/non-writing) of gradationdata and a blinking state (ON/OFF) of the illumination device. Awaveform “a” indicates a writing state of gradation data in the area B1,and a waveform “b” indicates a writing state of gradation data in thearea A1. A waveform “c” indicates a writing state of gradation data inthe area B2, and a waveform “d” indicates a writing state of gradationdata in the area A2. Besides, a waveform “e” indicates a blinking stateof the cold cathode fluorescent lamp 102 a, and a waveform “f” indicatesa blinking state of the cold cathode fluorescent lamp 102 b. As shown inFIG. 60, the light source control part 132 synchronizes with the latchpulse signal LP and causes the cold cathode fluorescent lamps 102 a and102 b to emit light for a specified time at a blinking frequency equalto a frame frequency (for example, 60 Hz). Besides, the light sourcecontrol part 132 causes a timing at which light emission brightness ofthe cold cathode fluorescent lamp 102 a is made maximum to be differentfrom a timing at which light emission brightness of the cold cathodefluorescent lamp 102 b is made maximum by about 8.4 msec (½ period).

The gradation data is written into the pixels of the areas B1 and B2substantially at the same timing. The liquid crystal display device ofthis example is of the multi-scan type, and the gate driver 12 outputsthe gate pulse GP in the order of the gate bus lines 6-1, 6-(N/2+1),6-2, 6-(N/2+2), . . . . That is, the gate bus lines 6 of the areas B1and B2 are alternately scanned. Besides, after the ½ period has passedsince the gate pulse GP was outputted to the gate bus line 6-1, the gatepulse GP is outputted to the gate bus line 6-(N/4+1), and thereafter,scanning is performed in the order of the gate bus lines 6-(3×N/4+1),6-(N/4+2), 12-(3×N/4+2) . . . .

After a specified time has passed since the gradation data were writteninto the pixels of the areas B1 and B2, the cold cathode fluorescentlamp 102 b for causing the light-emitting areas B1 and B2 to emit lightis turned on. Besides, after the cold cathode fluorescent lamp 102 b isturned off, the gradation data are written into the pixels of the areasB1 and B2. Similarly, after a specified time has passed since thegradation data were written into the pixels of the areas A1 and A2, thecold cathode fluorescent lamp 102 a for causing the light-emitting areasA1 and A2 to emit light is turned on. Besides, after the cold cathodefluorescent lamp 102 a is turned off, the gradation data are writteninto the pixels of the areas A1 and A2. As stated above, the coldcathode fluorescent lamp at the side of the areas in which the gradationdata are written is turned off. In the liquid crystal display device,since it takes a time of several msec to several tens msec until aliquid crystal molecule is inclined at a specified inclination anglefrom the writing of the gradation data into the pixel, when a time fromthe writing of the gradation data to the lighting of the cold cathodefluorescent lamp is secured to the extent possible, more excellentdisplay quality of a motion picture can be obtained. Thus, in thisexample, immediately after the cold cathode fluorescent lamp 102 a (102b) is turned off, the writing (rewriting) of gradation data into theareas A1, A2 (B1, B2) is started, and the time from the end of thewriting of the gradation data into the areas A1 and A2 (B1 and B2) tothe lighting of the cold cathode fluorescent lamp 102 a (102 b) issecured as the response time of the liquid crystal molecule.

In this example, although the lighting times of the cold cathodefluorescent lamps 102 a and 102 b are made equal to each other, thelighting times of the cold cathode fluorescent lamps 102 a and 102 b maybe made different from each other. Besides, in this example, althoughthe cold cathode fluorescent lamps 102 a and 102 b are turned on/off atthe specified frequency, the light emission brightnesses of the coldcathode fluorescent lamps 102 a and 102 b may be changed at a specifiedfrequency.

The illumination device according to this example is of the sidelighttype using the cold cathode fluorescent lamps 102 a and 102 b as thelinear light sources. Thus, the excellent display quality without unevenbrightness can be obtained. Besides, in the illumination deviceaccording to this example, even if the light-emitting area is divided inparallel to the long side direction of the light guide plate 100, thecold cathode fluorescent lamps 102 a and 102 b can be disposed while thetube axial direction is made substantially parallel to the long sidedirection of the light guide plate 100. Thus, the linear light sourcehaving a relatively large light emission quantity and a long length canbe used. Accordingly, the scan type illumination device having a highbrightness can be realized, and also when a motion picture is displayed,excellent display quality without contour blurring can be obtained.

FIG. 61 is a block diagram showing a modified example of the structureof the liquid crystal display device according to this example. As shownin FIG. 61, in this modified example, a gate driver 12 for driving gatebus lines 6-1 to 6-(N/2) of areas B1 and A1 and a gate driver 12′ fordriving gate bus lines 6-(N/2+1) to 6-N of areas B2 and A2 are providedto be independent of each other. Both the gate drivers 12 and 12′ areconnected to a control circuit 16. The gate driver 12 synchronizes witha latch pulse LP inputted from the control circuit 16 to output a gatepulse GP to the gate bus line 6-1, and at the same time, the gate driver12′ outputs a gate pulse GP to the gate bus line 6-(N/2+1). In this way,in this modified example, the gate driver 12 scans in the order of thegate bus lines 6-1, 6-2, . . . , 6-(N/2), and at the same time, the gatedriver 12′ can scan in the order of the gate bus lines 6-(N/2+1),6-(N/2+2), . . . , 6-N. Also by this modified example, the same effectas the above example can be obtained.

Example 5-2

First, an illumination device according to example 5-2 of thisembodiment will be described with reference to FIG. 62. FIG. 62 shows asectional structure of the illumination device according to thisexample. As shown in FIG. 62, a light guide plate 100 includes fourlight-emitting areas B1, A1, B2 and A2 divided substantially in parallelto the tube axial direction of cold cathode fluorescent lamps 102 a and102 b. The light-emitting area B1 is disposed at the side of the coldcathode fluorescent lamp 102 a, and the light-emitting area A1 isdisposed to be adjacent to the light-emitting area B1. Thelight-emitting area B2 is disposed to be adjacent to the light-emittingarea A1, and the light-emitting area A2 is disposed at the side of thecold cathode fluorescent lamp 102 b. The light-emitting areas B1, A1, B2and A2 of the light guide plate 100 are integrally formed, and a slit isnot formed at boundaries of the respective light-emitting areas B1, A1,B2 and A2.

In the light guide plate 100, an opposite surface 114 is inclined at aspecified inclination angle with respect to a light emission surface112, and is formed into different wedge shapes for the respective areas.The light guide plate 100 of the light-emitting areas A1 and A2 isformed into such a wedge shape that the thickness at the side of a sideend where the cold cathode fluorescent lamp 102 a is disposed is thick,and the thickness at the side of a side end where the cold cathodefluorescent lamp 102 b is disposed is thin. The light guide plate 100 ofthe light-emitting areas B1 and B2 is formed into such a wedge shapethat the thickness at the side of the side end where the cold cathodefluorescent lamp 102 a is disposed is thin, and the thickness at theside of the side end where the cold cathode fluorescent lamp 102 b isdisposed is thick. For example, the inclination angles of the oppositesurface 114 of the areas A1 and B2 are small as compared with theinclination angles of the opposite surface 114 of the areas B1 and A2.The wedge shapes of the light guide plate 100, together with a lightscattering element, function as light extraction elements.

In the light-emitting areas B1 and B2, light guided through the lightguide plate 100 from the side of the cold cathode fluorescent lamp 102 ais scattered by a scattering layer 116 when it is reflected at theopposite surface 114. However, the light is concentrated by the wedgeshape of the light guide plate 100 each time it is reflected, and theincident angle with respect to the light emission surface 112 becomeslarge. Thus, the light guided from the side of the cold cathodefluorescent lamp 102 a is kept being guided in the light-emitting areasB1 and B2, and is not emitted to the outside of the light guide plate100 much. On the other hand, light guided from the side of the coldcathode fluorescent lamp 102 b is scattered by the scattering layer 116when it is reflected at the opposite surface 114, and the incident anglewith respect to the light emission surface 112 becomes small by thewedge shape of the light guide plate 100 each time it is reflected atthe opposite surface 114. Thus, part of the light guided from the sideof the cold cathode fluorescent lamp 102 b is not kept being guided inthe light-emitting areas B1 and B2, and is emitted to the outside of thelight guide plate 100.

In the light-emitting areas A1 and A2, light guided through the lightguide plate 100 from the side of the cold cathode fluorescent lamp 102 bis scattered by the scattering layer 116 when it is reflected at theopposite surface 114. However, the light is concentrated by the wedgeshape of the light guide plate 100 each time it is reflected, and theincident angle with respect to the light emission surface 112 becomeslarge. Thus, the light guided from the side of the cold cathodefluorescent lamp 102 b is kept being guided in the light-emitting areasA1 and A2, and is not emitted to the outside of the light guide plate100 much. On the other hand, light guided from the side of the coldcathode fluorescent lamp 102 a is scattered by the scattering layer 116when it is reflected at the opposite surface 114, and the incident anglewith respect to the light emission surface 112 becomes small by thewedge shape of the light guide plate 100 each time it is reflected atthe opposite surface 114. Thus, part of the light guided from the sideof the cold cathode fluorescent lamp 102 a is not kept being guided inthe light-emitting areas A1 and A2, and is emitted to the outside of thelight guide plate 100.

As stated above, in the light-emitting areas A1 and A2, the light guidedfrom the side of the cold cathode fluorescent lamp 102 a is moreextracted, and in the light-emitting areas B1 and B2, the light guidedfrom the side of the cold cathode fluorescent lamp 102 b is moreextracted. Besides, in the light guide plate 100, light can be extractedalmost uniformly in all the light-emitting areas B1, A1, B2 and A2.According to this example, the same effect as the example 5-1 can beobtained.

Example 5-3

Next, an illumination device according to example 5-3 of this embodimentwill be described with reference to FIG. 63. FIG. 63 shows a sectionalstructure of the illumination device according to this example. As shownin FIG. 63, a light guide plate 100 includes four light-emitting areasA1, B1, A2 and B2 divided substantially in parallel to the tube axialdirection of cold cathode fluorescent lamps 102 a and 102 b. Thelight-emitting area A1 is disposed at the side of the cold cathodefluorescent lamp 102 a, and the light-emitting area B1 is disposed to beadjacent to the light-emitting area A1. The light-emitting area A2 isdisposed to be adjacent to the light-emitting area B1, and thelight-emitting area B2 is disposed at the side of the cold cathodefluorescent lamp 102 b. The light-emitting areas A1, B1, A2 and B2 ofthe light guide plate 100 are integrally formed, and a slit is notformed at boundaries of the respective light-emitting areas A1, B1, A2and B2.

In the light guide plate 100, an opposite surface 114 is inclined atspecified inclination angles with respect to a light emission surface112, and is formed into different wedge shapes for the respective areas.The light guide plate 100 of the light-emitting areas A1 and A2 isformed into such a wedge shape that the thickness at the side of a sideend where the cold cathode fluorescent lamp 102 a is disposed is thick,and the thickness at the side of a side end where the cold cathodefluorescent lamp 102 b is disposed is thin. The light guide plate 100 ofthe light-emitting areas B1 and B2 is formed into such a wedge shapethat the thickness at the side of the side end where the cold cathodefluorescent lamp 102 a is disposed is thin, and the thickness at theside of the side end where the cold cathode fluorescent lamp 102 b isdisposed is thick. For example, the inclination angles of the oppositesurface 114 of the areas A2 and B1 are small as compared with theinclination angles of the opposite surface 114 of the areas A1 and B2.The wedge shapes of the light guide plate 100, together with a lightscattering element, function as light extraction elements.

In the light-emitting areas B1 and B2, light guided through the lightguide plate 100 from the side of the cold cathode fluorescent lamp 102 ais scattered by a scattering layer 116 when it is reflected at theopposite surface 114. However, the light is concentrated by the wedgeshape of the light guide plate 100 each time it is reflected, and theincident angle with respect to the light emission surface 112 becomeslarge. Thus, the light guided from the side of the cold cathodefluorescent lamp 102 a is kept being guided in the light-emitting areasB1 and B2, and is not emitted to the outside of the light guide plate100 much. On the other hand, light guided from the side of the coldcathode fluorescent lamp 102 b is scattered by the scattering layer 116when it is reflected at the opposite surface 114, and the incident anglewith respect to the light emission surface 112 becomes small by thewedge shape of the light guide plate 100 each time it is reflected atthe opposite surface 114. Thus, part of the light guided from the sideof the cold cathode fluorescent lamp 102 b is not kept being guided inthe light-emitting areas B1 and B2, and is emitted to the outside of thelight guide plate 100.

In the light-emitting areas A1 and A2, light guided through the lightguide plate 100 from the side of the cold cathode fluorescent lamp 102 bis scattered by the scattering layer 116 when it is reflected at theopposite surface 114. However, the light is concentrated by the wedgeshape of the light guide plate 100 each time it is reflected, and theincident angle with respect to the light emission surface 112 becomeslarge. Thus, the light guided from the side of the cold cathodefluorescent lamp 102 b is kept being guided in the light-emitting areasA1 and A2, and is not emitted to the outside of the light guide plate100 much. On the other hand, light guided from the side of the coldcathode fluorescent lamp 102 a is scattered by the scattering layer 116when it is reflected at the opposite surface 114, and the incident anglewith respect to the light emission surface 112 becomes small by thewedge shape of the light guide plate 100 each time it is reflected atthe opposite surface 114. Thus, part of the light guided from the sideof the cold cathode fluorescent lamp 102 a is not kept being guided inthe light-emitting areas A1 and A2, and is emitted to the outside of thelight guide plate 100.

As stated above, in the light-emitting areas A1 and A2 of the lightguide plate 100, the light guided from the side of the cold cathodefluorescent lamp 102 a is more extracted, and in the light-emittingareas B1 and B2, the light guided from the side of the cold cathodefluorescent lamp 102 b is more extracted. Besides, in the light guideplate 100, light can be extracted almost uniformly in all thelight-emitting areas B1, A1, B2 and A2.

According to this example, the same effect as the example 5-1 can beobtained. Besides, in the liquid crystal display device using thebacklight unit 130 according to this example, the timing of brightnessmodulation of the cold cathode fluorescent lamps 102 a and 102 b is madeopposite to the timing of brightness modulation of the example 5-1 shownin FIG. 60, so that the scan type illumination device having highbrightness can be realized, and also when a motion picture is displayed,excellent display quality without contour blurring can be obtained.

Example 5-4

Next, an illumination device according to example 5-4 of this embodimentwill be described with reference to FIG. 64. FIG. 64 shows a sectionalstructure of the illumination device according to this example. As shownin FIG. 64, a light guide plate 100 includes four light-emitting areasA1, B1, A2 and B2 divided substantially in parallel to the tube axialdirection of cold cathode fluorescent lamps 102 a and 102 b. Thelight-emitting area A1 is disposed at the side of the cold cathodefluorescent lamp 102 a, and the light-emitting area B1 is disposed to beadjacent to the light-emitting area A1. The light-emitting area A2 isdisposed to be adjacent to the light-emitting area B1, and thelight-emitting area B2 is disposed at the side of the cold cathodefluorescent lamp 102 b. The light-emitting areas A1, B1, A2 and B2 ofthe light guide plate 100 are integrally formed, and a slit is notformed at boundaries of the respective light-emitting areas A1, B1, A2and B2. An opposite surface 114 of the light guide plate 100 is formedinto a prism shape, and the prism shape functions as a light extractionelement for extracting light.

The opposite surface 114 of the light-emitting areas B1 and B2 has sucha prism shape that light from the side of the cold cathode fluorescentlamp 102 a is not incident on the prism surface 118, but is guided tothe side of the cold cathode fluorescent lamp 102 b as it is. The prismsurface 118 is formed to have an inclination angle of, for example, 40°to 45° with respect to the light emission surface 112. On the otherhand, light from the side of the cold cathode fluorescent lamp 102 b isincident on the prism surface 118 at a certain probability. The lightincident on the prism surface 118 comes not to satisfy the totalreflection condition and is emitted to the outside of the light guideplate 100 by reflection or refraction.

The opposite surface 114 of the light-emitting areas A1 and A2 has sucha prism shape that light from the side of the cold cathode fluorescentlamp 102 b is not incident on a prism surface 119, but is guided to theside of the cold cathode fluorescent lamp 102 b as it is. The prismsurface 119 is formed to have an inclination angle of, for example, 40°to 45° with respect to the light emission surface 112. On the otherhand, light from the cold cathode fluorescent lamp 102 a is incident onthe prism surface 119 at a certain probability. The light incident onthe prism surface 119 comes not to satisfy the total reflectioncondition and is emitted to the outside of the light guide plate 100 byreflection or refraction.

As stated above, in the light-emitting areas A1 and A2 of the lightguide plate 100, the light guided from the side of the cold cathodefluorescent lamp 102 a is more extracted, and in the light-emittingareas B1 and B2, the light guided from the side of the cold cathodefluorescent lamp 102 b is more extracted. Besides, in the light guideplate 100, light can be extracted almost uniformly in all thelight-emitting areas B1, A1, B2 and A2. According to this example, thesame effect as the example 5-1 can be obtained.

Example 5-5

Next, a liquid crystal display device according to example 5-5 of thisembodiment will be described with reference to FIG. 65. FIG. 65 shows asectional structure of the liquid crystal display device according tothis example. As shown in FIG. 65, the liquid crystal display deviceaccording to this example is of a front light system, and includes areflection type LCD panel 2 and a front light unit 131. A light guideplate 100 of the front light unit 131 includes four light-emitting areasB1, A1, B2 and A2 divided substantially in parallel to the tube axialdirection of cold cathode fluorescent lamps 102 a and 102 b. Thelight-emitting area B1 is disposed at the side of the cold cathodefluorescent lamp 102 a, and the light-emitting area A1 is disposed to beadjacent to the light-emitting area B1. The light-emitting area B2 isdisposed to be adjacent to the light-emitting area A1, and thelight-emitting area A2 is disposed at the side of the cold cathodefluorescent lamp 102 b. The light-emitting areas B1, A1, B2 and A2 ofthe light guide plate 100 are integrally formed, and a slit is notformed at boundaries of the respective light-emitting areas B1, A1, B2and A2. An opposite surface 114 of the light guide plate 100 is formedinto a prism shape. The prism shape functions as a light extractionelement for extracting light.

In the front light system, it is not wise to use a scattering layer 116or the like as a light extraction element. This is because scatteredlight by the scattering layer 116 is not emitted in the directionvertical to the LCD panel 2, so that it becomes a cause of low contrastand low brightness. Besides, since light is directly emitted to anobserver side as well, it becomes a cause of stray light and lowcontrast, and display quality is lowered. Accordingly, in this example,the light extraction element is made the prism shape. Besides, the lightguide plate 100 and a polarizing plate 141 are bonded to each other, andare further bonded to the LCD panel 2, so that interface reflection islowered and the display quality can be further improved.

Example 5-6

Next, an illumination device according to example 5-6 of this embodimentand a liquid crystal display device using the same will be describedwith reference to FIGS. 66 to 68. FIG. 66 shows a sectional structure ofthe liquid crystal display device according to this example. FIG. 67shows a sectional structure of the illumination device according to thisexample. As shown in FIGS. 66 and 67, a backlight unit 130 according tothis example includes two light guide plates 100 and 100′ which arelaminated and disposed. The light guide plates 100 and 100′ include fourlight-emitting areas B1, B2, A1 and A2. A cold cathode fluorescent lamp102 a is disposed at one side end face (left end face in FIGS. 66 and67) of the lower light guide plate 100 in the drawing. Besides, a coldcathode fluorescent lamp 102 b is disposed at the other side end face(right end face in FIGS. 66 and 67) of the light guide plate 100. Thelight guide plate 100 includes a light guide area for guiding light fromthe cold cathode fluorescent lamps 102 a and 102 b. In the light guideplate 100 of the light-emitting area B1, an opposite surface 114 isinclined with respect to a light emission surface 112 so that thethickness at the side of the cold cathode fluorescent lamp 102 a is thinand the thickness at the side of the cold cathode fluorescent lamp 102 bis thick, and is formed into a wedge shape. Besides, in the light guideplate 100 of the light-emitting area A1, an opposite surface 114 isinclined with respect to the light emission surface 112 so that thethickness at the cold cathode fluorescent lamp 102 a is thick and thethickness at the cold cathode fluorescent lamp 102 b is thin, and isformed into a wedge shape. Scattering layers 116 as light scatteringelements are formed on the opposite surfaces 114 of the light-emittingareas A1 and B1. The light guide plate 100 includes the light guide areafor guiding light from the cold cathode fluorescent lamps 102 a and 102b.

A cold cathode fluorescent lamp 102 a′ is disposed at one side end face(left end face in FIGS. 66 and 67) of the light guide plate 100′laminated and disposed at the liquid crystal display panel 2 side of thelight guide plate 100. Besides, a cold cathode fluorescent lamp 102 b′is disposed at the other side end face (right end face in FIGS. 66 and67) of the light guide plate 100′. The light guide plate 100′ includes alight guide area for guiding light from the cold cathode fluorescentlamps 102 a′ and 102 b′. In the light guide plate 100′ of thelight-emitting area B2, an opposite surface 114 is inclined with respectto a light emission surface 112 so that the thickness at the side of thecold cathode fluorescent lamp 102 a′ is thin and the thickness at theside of the cold cathode fluorescent lamp 102 b′ is thick, and is formedinto a wedge shape. Besides, in the light guide plate 100′ of thelight-emitting area A2, an opposite surface 114 is inclined with respectto the light emission surface 112 so that the thickness at the side ofthe cold cathode fluorescent lamp 102 a′ is thick and the thickness atthe side of the cold cathode fluorescent lamp 102 b′ is thin, and isformed into a wedge shape. Scattering layers 116 as light scatteringelements are formed on the opposite surfaces 114 of the areas A2 and B2.

In the light-emitting area B1 of the light guide plate 100, light guidedfrom the side of the cold cathode fluorescent lamp 102 b is scattered bythe scattering layer 116 when it is reflected at the opposite surface114, and the incident angle with respect to the light emission surface112 becomes small by the wedge shape of the light guide plate 100 eachtime it is reflected at the opposite surface 114. Thus, most of thelight guided from the side of the cold cathode fluorescent lamp 102 b isnot kept being guided in the light-emitting area B1, and is emitted tothe outside of the light guide plate 100. On the other hand, althoughlight guided from the side of the cold cathode fluorescent lamp 102 a tothe light-emitting area B1 is scattered by the scattering layer 116 whenit is reflected at the opposite surface 114, the light is concentratedby the wedge shape of the light guide plate 100 each time it isreflected, and the incident angle with respect to the light emissionsurface 112 becomes large. Thus, the light guided from the side of thecold cathode fluorescent lamp 102 a to the light-emitting area B1 iskept being guided in the light-emitting area B1, and is not emitted tothe outside of the light guide plate 100 much. That is, thelight-emitting area B1 of the light guide plate 100 has a relation of(extracted light quantity from the side of the cold cathode fluorescentlamp 102 b/guided light quantity from the side of the cold cathodefluorescent lamp 102 b)>(extracted light quantity from the side of thecold cathode fluorescent lamp 102 a/guided light quantity from the sideof the cold cathode fluorescent lamp 102 a).

In the light-emitting area A1 of the light guide plate 100, light guidedfrom the side of the cold cathode fluorescent lamp 102 a is scattered bythe scattering layer 116 when it is reflected at the opposite surface114, and the incident angle with respect to the light emission surface112 becomes small by the wedge shape of the light guide plate 100 eachtime it is reflected at the opposite surface 114. Thus, most of thelight guided from the side of the cold cathode fluorescent lamp 102 isnot kept being guided in the light-emitting area A1, and is emitted tothe outside of the light guide plate 100. On the other hand, althoughlight guided from the side of the cold cathode fluorescent lamp 102 b tothe light-emitting area A1 is scattered by the scattering layer 116 whenit is reflected at the opposite surface 114, the light is concentratedby the wedge shape of the light guide plate 100 each time it isreflected, and the incident angle with respect to the light emissionsurface 112 becomes large. Thus, the light guided from the side of thecold cathode fluorescent lamp 102 b to the light-emitting area A1 iskept being guided in the light-emitting area A1, and is not emitted tothe outside of the light guide plate 100 much. That is, thelight-emitting area A1 of the light guide plate 100 has a relation of(extracted light quantity from the side of the cold cathode fluorescentlamp 102 a/guided light quantity from the side of the cold cathodefluorescent lamp 102 a)>(extracted light quantity from the side of thecold cathode fluorescent lamp 102 b/guided light quantity from the sideof the cold cathode fluorescent lamp 102 b).

In the light-emitting area B2 of the light guide plate 100′, lightguided from the side of the cold cathode fluorescent lamp 102 b′ isscattered by the scattering layer 116 when it is reflected at theopposite surface 114, and the incident angle with respect to the lightemission surface 112 becomes small by the wedge shape of the light guideplate 100 each time it is reflected at the opposite surface 114. Thus,most of the light guided from the side of the cold cathode fluorescentlamp 102 b′ is not kept being guided in the light-emitting area B2, andis emitted to the outside of the light guide plate 100. On the otherhand, although light guided from the side of the cold cathodefluorescent lamp 102 a′ to the light-emitting area B2 is scattered bythe scattering layer 116 when it is reflected at the opposite surface114, the light is concentrated by the wedge shape of the light guideplate 100 each time it is reflected, and the incident angle with respectto the light emission surface 112 becomes large. Thus, the light guidedfrom the side of the cold cathode fluorescent lamp 102 a′ to thelight-emitting area B2 is kept being guided in the light-emitting areaB2, and is not emitted to the outside of the light guide plate 100 much.That is, the light-emitting area B2 of the light guide plate 100′ has arelation of (extracted light quantity from the side of the cold cathodefluorescent lamp 102 b′/guided light quantity from the side of the coldcathode fluorescent lamp 102 b′)>(extracted light quantity from the sideof the cold cathode fluorescent lamp 102 a′/guided light quantity fromthe side of the cold cathode fluorescent lamp 102 a′).

In the light-emitting area A2 of the light guide plate 100′, lightguided from the side of the cold cathode fluorescent lamp 102 a′ isscattered by the scattering layer 116 when it is reflected at theopposite surface 114, and the incident angle with respect to the lightemission surface 112 becomes small by the wedge shape of the light guideplate 100 each time it is reflected at the opposite surface 114. Thus,most of the light guided from the side of the cold cathode fluorescentlamp 102 a′ is not kept being guided in the light-emitting area A2, andis emitted to the outside of the light guide plate 100. On the otherhand, although light guided from the side of the cold cathodefluorescent lamp 102 b′ to the light-emitting area A2 is scattered bythe scattering layer 116 when it is reflected at the opposite surface114, the light is concentrated by the wedge shape of the light guideplate 100 each time it is reflected, and the incident angle with respectto the light emission surface 112 becomes large. Thus, the light guidedfrom the side of the cold cathode fluorescent lamp 102 b′ to thelight-emitting area A2 is kept being guided in the light-emitting areaA2, and is not emitted to the outside of the light guide plate 100 much.That is, the light-emitting area B2 of the light guide plate 100′ has arelation of (extracted light quantity from the side of the cold cathodefluorescent lamp 102 a′/guided light quantity from the side of the coldcathode fluorescent lamp 102 a′)>(extracted light quantity from the sideof the cold cathode fluorescent lamp 102 b′/guided light quantity fromthe side of the cold cathode fluorescent lamp 102 b′).

The light-emitting areas B2 and A2 of the light guide plate 100 arenon-light-extraction areas in which both the light from the side of thecold cathode fluorescent lamp 102 a and the light from the side of thecold cathode fluorescent lamp 102 b are hardly extracted. Besides, thelight-emitting areas B1 and A1 of the light guide plate 100′ arenon-light-extraction areas in which both the light from the side of thecold cathode fluorescent lamp 102 a′ and the light from the side of thecold cathode fluorescent lamp 102 b′ are hardly extracted.

As stated above, in the light-emitting area A1 of the light guide plate100, the light guided from the side of the cold cathode fluorescent lamp102 a is more extracted, and in the light-emitting area B1, the lightguided from the side of the cold cathode fluorescent lamp 102 b is moreextracted. In the light-emitting area A2 of the light guide plate 100′,the light guided from the side of the cold cathode fluorescent lamp 102a′ is more extracted, and in the light-emitting area B2, the lightguided from the side of the cold cathode fluorescent lamp 102 b′ is moreextracted. Besides, when the light guide plate 100 and 100′ arelaminated and disposed, light is almost uniformly extracted in all thelight-emitting areas B1, A1, B2 and A2.

FIG. 68 shows a driving method of the illumination device according tothis example and the liquid crystal display device using the same. Thehorizontal axis direction indicates time, and the vertical axisdirection indicates a writing state (writing/non-writing) of gradationdata and a blinking state (ON/OFF) of the backlight unit 130. A waveform“a” indicates a writing state of gradation data in the light-emittingarea B1, and a waveform “b” indicates a writing state of gradation datain the area B2. A waveform “c” indicates a writing state of gradationdata in the area A1, and a waveform “d” indicates a writing state ofgradation data in the area A2. Besides, a waveform “e” indicates ablinking state of the cold cathode fluorescent lamp 102 b, and awaveform “f” indicates a blinking state of the cold cathode fluorescentlamp 102 b′. A waveform “g” indicates a blinking state of the coldcathode fluorescent lamp 102 a, and a waveform “h” indicates a blinkingstate of the cold cathode fluorescent lamp 102 a′.

As shown in FIG. 68, a light source control part 132 (not shown in FIG.66) synchronizes with a latch pulse signal LP and causes the coldcathode fluorescent lamps 102 a, 102 b, 102 a′ and 102 b′ to emit lightfor a specified time at a blinking frequency equal to a frame frequency(for example, 60 Hz). Besides, the light source control part 132 causesa timing at which the light emission brightness of the cold cathodefluorescent lamp 102 b is made maximum to be different from a timing atwhich the light emission brightness of the cold cathode fluorescent lamp102 b′ is made maximum by about 4.2 msec (¼ period). Similarly, a timingat which the light emission brightness of the cold cathode fluorescentlamp 102 b′ is made maximum is different from a timing at which thelight emission brightness of the cold cathode fluorescent lamp 102 a ismade maximum by about 4.2 msec, and a timing at which the light emissionbrightness of the cold cathode fluorescent lamp 102 a is made maximum isdifferent from a timing at which the light emission brightness of thecold cathode fluorescent lamp 102 a′ is made maximum by about 4.2 msec.Besides, a timing at which the light emission brightness of the coldcathode fluorescent lamp 102 a′ is made maximum is different from atiming at which the light emission brightness of the cold cathodefluorescent lamp 102 b is made maximum by about 4.2 msec.

After a specified time has passed since gradation data was written intopixels of the area B1, the cold cathode fluorescent lamp 102 b forcausing the light-emitting area B1 to emit light is turned on. Besides,after the cold cathode fluorescent lamp 102 b is turned off, gradationdata is written into pixels of the area B1. After a specified time haspassed since gradation data was written into pixels of the area B2, thecold cathode fluorescent lamp 102 b′ for causing the light-emitting areaB2 to emit light is turned on. Besides, after the cold cathodefluorescent lamp 102 b′ is turned off, gradation data is written intopixels of the area B2. Similarly, a specified time has passed sincegradation data was written into pixels of the area A1, the cold cathodefluorescent lamp 102 a for causing the light-emitting area A1 to emitlight is turned on. Besides, after the cold cathode fluorescent lamp 102a is turned off, gradation data is written into pixels of the area A1. Aspecified time has passed since gradation data was written into pixelsof the area A2, the cold cathode fluorescent lamp 102 a′ for causing thelight-emitting area A2 to emit light is turned on. Besides, after thecold cathode fluorescent lamp 102 a′ is turned off, gradation data iswritten into pixels of the area A2.

As stated above, the cold cathode fluorescent lamp for illuminating thearea into which the gradation data is written is turned off. In theliquid crystal display device, since it takes a time of several msec toseveral tens msec until a liquid crystal molecule is inclined at aspecified inclination angle from the writing of the gradation data intothe pixel, when a time from the writing of the gradation data of acertain area to the lighting of the cold cathode fluorescent lamp forilluminating the area is secured to the extent possible, more excellentdisplay quality of a motion picture can be obtained. Thus, in thisexample, immediately after the cold cathode fluorescent lamp 102 a isturned off, the writing of the gradation data is started.

According to this example, the same effect as the example 5-1 can beobtained. Besides, in this embodiment, contrary to the example 5-1, amulti-scan type liquid crystal display device is not required, thescan-type illumination device and the liquid crystal display device canbe realized without complicating the driving circuit. Incidentally, inthis example, although the light guide plate 100 and 100′ include fourdivided light-emitting areas A1, A2, B1 and B2, the number of dividedareas is arbitrary.

According to this embodiment, it is possible to realize the scan typeillumination device and the liquid crystal display device, which has thesimple structure, is small, thin and light, and has uniform brightnessand color. Besides, according to this embodiment, the liquid crystaldisplay device without contour blurring and excellent in the motionpicture quality can be realized.

Sixth Embodiment

An illumination device according to a sixth embodiment of the inventionand a liquid crystal display device using the same will be describedwith reference to FIGS. 69 to 73. This embodiment is characterized by apolarizing plate bonded to a liquid crystal display device or anillumination device used for that, and is characterized by amanufacturing method in a case where the polarizing plate is bonded to apanel surface of the liquid crystal display device or to a light guideplate of the illumination device.

In general, a transmission liquid crystal display device is constructedsuch that transmissivity of light incident from the rear surface of aliquid crystal panel is modulated in a liquid crystal layer and thelight is emitted to the panel surface, and a backlight unit as anillumination device is disposed at the rear side of the liquid crystalpanel. On the other hand, a reflection liquid crystal display device fora mobile use is constructed such that outside light is incident from thesurface of a liquid crystal panel, is made to pass through a liquidcrystal layer and to be reflected at a reflection electrode, ismodulated in the liquid crystal layer and is emitted to the panelsurface.

In general, in the reflection liquid crystal display device, as anauxiliary illumination light source at the time of less outside light, afront light unit (for example, see the example 5-5 (FIG. 65) of thefifth embodiment) is disposed at the side of a liquid crystal panelsurface. The front light unit includes a transparent plate-like lightguide plate disposed at the side of the liquid crystal panel surface,and a light source disposed at least the side of one side surface of thelight guide plate. A prism is formed stepwise at the surface side(outside light incident side) of the light guide plate at a small pitchof, for example, 1 mm or less, and incident light from a light source atthe side of the light guide plate is reflected, refracted andtransmitted in the in-plane direction, and almost vertical light isemitted to the whole surface of the liquid crystal panel surface. Sincethe light guide plate is required to have high transmissivity, to beeasily molded, and to be light, the same acryl material as the lightguide plate for the backlight unit is often used.

A polarizing plate is disposed between the light emission surface of thelight guide plate at the side of the liquid crystal panel surface andthe liquid crystal panel surface. When this polarizing plate is bondedto the light emission surface of the light guide plate at the side ofthe liquid crystal panel surface, it is possible to absorb unnecessarylight incident on the liquid crystal panel surface from the light guideplate at a relatively large incident angle, to suppress the degradation(black floating or the like) of picture quality, and to obtain a highcontrast display.

Since the front light unit is mainly used for a small liquid crystaldisplay device, the light guide plate is required to be light and small.Thus, the light guide plate is formed of a very thin plate having athickness of about 1 mm and has such a structure that it is easilydeformed. On the other hand, in the polarizing plate bonded to the lightguide plate, a heat shrinkage of 0.3% to 0.5% occurs under a hightemperature. Thus, there arises a problem that when the polarizing plateis heat shrunk under a high temperature, the light guide plate isdeformed. For example, in the case where a liquid crystal display deviceis left in, for example, an automobile on a summer day and is put undera high temperature on the day, the polarizing plate is shrunk and bendsthe light guide plate, and even if it is again put in the place of roomtemperature, the shrinkage is kept as it is, and therefore, thedeformation of the light guide plate remains. Although a protectioncover to prevent the surface prism of the light guide plate from beingsoiled is provided at the outside light incident side of the light guideplate of the front light unit, when the light guide plate is bent andcomes in contact with this protection cover, both are rubbed and thelight guide plate is scratched, and a bad influence is given on thedisplay quality to cause uneven brightness or the like. In order toavoid this, when a distance between the light guide plate and theprotection cover is previously made long, a gap of about 5 mm isrequired, which increases the thickness of the device. Besides, when thelight guide plate itself is deformed, the center of the light guideplate expands to become a crest, circular moire fringes are produced andthe display quality is degraded.

In order to solve this problem, in this embodiment, it has been foundthat the heat shrinkage of the polarizing plate is irreversible, and theheat shrinkage is saturated at 0.3 to 0.5%, and therefore, thepolarizing plate is previously subjected to heat treatment to causeirreversible shrinkage and then used. The heat treatment is performed insuch a way that the polarizing plate is left in a specified temperatureenvironment for a specific time. At this time, when the heat treatmenttemperature is made 100° C. or higher, the degradation of the polarizingplate itself occurs so that the degree of polarization is rapidlylowered and the contrast of a display is lowered, and accordingly,attention must be paid. Besides, when the heat treatment temperaturebecomes 40° C. or less, since the progress of the heat shrinkage of thepolarizing plate becomes slow, it takes a long time to perform the heattreatment, and attention must be paid in an actual manufacture process.

When the polarizing plate is subjected to a suitable heat treatmentwhile attention is given to such a range of the heat treatmenttemperature, even in the case where the liquid crystal display device isleft under a high temperature, the deformation quantity of the lightguide plate can be made small, and accordingly, the distance between thelight guide plate and the protection cover is made small, and the devicevolume can be made small. Besides, since the deformation of the lightguide plate can be made small, the degradation of the display qualitydue to the moire fringes can also be made slight. Further, when theenvironment temperature is returned to room temperature, the deformationof the light guide plate is returned to the original, so that thedisplay quality is also not damaged.

Hereinafter, a description will be given of specific examples. FIG. 69shows a manufacturing method of an illumination device according to thisembodiment. As shown in FIG. 69, first, at a polarizing plate heattreatment step 91, a polarizing plate is subjected to heat treatment ina constant temperature bath at a specified temperature. Thereafter, thetemperature is returned to the room temperature, and then a bonding step92 to the light guide plate is started, and the polarizing plate isbonded to the surface of the light guide plate by a bonding machine.Next, an autoclave treatment is performed (autoclave treatment step 93).Next, at an attachment step 94 of a lamp assembly, a light source andthe like are attached to the light guide plate, and a front light iscompleted.

Next, conditions and the like for suitably carrying out the polarizingplate heat treatment step 91 will be described in detail. First, anexamination is carried out on a change of wavelength (hereinafterreferred to as a cut wavelength shift amount) at which transmissivity ofthe polarizing plate in an absorption axis becomes 50% and a change ofshrinkage percentage according to a heat treatment temperature and aheat treatment time (see FIG. 70). It is known that the use uppertemperature of a polarizing plate recommended by a manufacture maker isusually about 70° C., and when it is exposed to a temperature higherthan that, the deterioration of the polarizing plate is accelerated. Thedeterioration of the polarizing plate is the deterioration of the degreeof polarization, and the degree of deterioration is found by measuringthe cut wavelength in the absorption axis and examining the shift (seeFIG. 71).

FIG. 70 shows the cut wavelength change in the polarizing plateabsorption axis with respect to the heat treatment time in the heattreatment of the polarizing plate in the illumination device accordingto this embodiment. The horizontal axis indicates the heat treatmenttime (hr), and the vertical axis indicates the cut wavelength shiftamount (nm). In the drawing, a broken line having a short pitchindicates data obtained when the heat treatment temperature to thepolarizing plate is 50° C. Similarly, an alternate long and short dashline indicates data obtained when the heat treatment temperature is 60°C., a thin solid line indicates data obtained when the heat treatmenttemperature is 70° C., and a broken line having a long pitch indicatesdata obtained when the heat treatment temperature is 100° C. Besides, athick solid line indicates the cut wavelength shift amount of apolarizing plate used for a 17-inch liquid crystal display device, whichis comparative data obtained for a case where the polarizing plate notsubjected to heat treatment is bonded to a light guide plate, and isdenoted by “in 17-inch device” in the drawing.

As shown in FIG. 70, the cut wavelength shift amount of “in 17-inchdevice” indicated by the thick solid line is −6 nm at the heat treatmentof 500 hr, and −11 nm at the heat treatment of 1000 hr. As compared withthis, in the polarizing plate subjected to heat treatment at atemperature of 50° C. or higher, as the heat treatment temperaturebecomes high, the cut wavelength shift amount in the same heat treatmenttime is increased, and the deterioration is accelerated. Here, it isunderstood that when the heat treatment temperature is 70° C. or lower,and the heat treatment time does not exceed 50 hr, the cut wavelengthshift amount is −11 nm or less, and is equivalent to the degradation of1000 hr in the comparative data of “in 17-inch device”. The time of 1000hr is 3% of the lifetime of the 17-inch liquid crystal display device,and is put in an allowable range in terms of the quantity ofdeterioration at the polarizing plate heat treatment.

FIG. 71 shows a transmission characteristic of the polarizing plate inan absorption axis direction in a case where the polarizing plate issubjected to heat treatment at 70° C. The horizontal axis indicates awavelength (mm), and the vertical axis indicates a transmissivity (%).In the drawing, a solid line indicates a transmission characteristic ina case where the heat treatment time is 2000 hours, and a broken lineindicates a transmission characteristic in a case where the heattreatment time is 0 hour (that is, heat treatment is not performed). Ascompared with the case where the heat treatment is not performed, thecut wavelength of the polarizing plate in the absorption axis is loweredfrom about 810 nm to about 785 nm.

FIG. 72 shows a change of shrinkage percentage of the polarizing platewith respect to a heat treatment time in the illumination deviceaccording to this embodiment. The horizontal axis indicates a heattreatment time (hr), and the vertical axis indicates a shrinkagepercentage. A solid line in the drawing indicates a case where the heattreatment temperature is 70° C., and a broken line indicates a casewhere the heat treatment temperature is 60° C. With respect to theshrinkage percentage of the polarizing plate, the lengths of thehorizontal and vertical sides of the polarizing plate are measuredbefore and after the heat treatment, and an average of the changes withrespect to the original length is calculated. As the heat treatmenttemperature becomes high, the shrinkage of the polarizing plate isaccelerated, and therefore, in this example, the changes at the heattreatment temperatures of 60° C. and 70° C. are indicated. Although theheat shrinkage percentages of both become identical in the case wherethe heat treatment time is 100 hr or more, the rate of the heatshrinkage is faster when the heat treatment temperature is 70° C., andthe shrinkage of the polarizing plate becomes almost saturated by thetreatment of 40 to 50 hr. Also with respect to the cut wavelength shiftamount in the polarizing plate absorption axis shown in FIG. 70, sinceit is apparent as described above that the heat treatment time of 50 hror less is preferable, it is understood that the heat treatment issuitable when the heat treatment temperature is 70° C. Besides, fromFIG. 72, when the heat treatment temperature is made 70° C., the heattreatment time of 40 hr in which the heat shrinkage is almost saturatedis desirable.

Then, the polarizing plate subjected to the heat treatment at the heattreatment temperature of 70° C. and the heat treatment time of 40 hr isbonded to the light guide plate, and the deformation quantity of thelight guide plate is measured using a thermal shock test machine.Specifically, four sides of a front light unit in which light sourcesare attached to ends of the light guide plate to which the polarizingplate is bonded, are fixed onto the liquid crystal panel and a thermalshock test of a temperature of 60° C. for 25 minutes and a temperatureof −20° C. for 35 minutes is performed. With respect to the deformationquantity of the light guide plate, a distance between a most raisedportion of the center of the light guide plate and an edge of the lightguide plate is measured and is made the deformation quantity.

FIG. 73 shows a relation between a thermal shock test time and a lightguide plate deformation quantity in the illumination device according tothis embodiment. The horizontal axis indicates a thermal shock test time(hr) and the vertical axis indicates a deformation quantity (mm) of alight guide plate. In the drawing, a solid line indicates a polarizingplate subjected to heat treatment, and a broken line indicates apolarizing plate not subjected to heat treatment.

In the conventional polarizing plate (broken line) which is notsubjected to the heat treatment, the deformation quantity is 4.6 mm whenthe thermal shock test time is 600 hr, and on the other hand, in thepolarizing plate (solid line) subjected to the heat treatment, thedeformation quantity is 1.0 mm when the shock test time is 600 hr, andthe deformation can be suppressed to 39% of the related art.

As described above, according to this embodiment, the polarizing plateis subjected to a suitable heat treatment to cause irreversible heatshrinkage in advance and then, it is bonded to a light guide plate, anda front light unit is manufactured. Especially, it is preferable that aheat shrinkage quantity α is in a range of 0<α≦0.3%. By doing so, evenin the case where the liquid crystal display device is left under a hightemperature, the deformation quantity of the light guide plate can begreatly suppressed. Accordingly, the distance between the light guideplate and the protection cover can be shortened by 1 to 2 mm, and thedevice volume can be made small. Besides, since the deformation quantityof the light guide plate is small, the moire fringes become slight, andwhen the environmental temperature is returned to the room temperature,the deformation is removed and the shape returns to an original one, andtherefore, the display quality is also not damaged.

Incidentally, in this embodiment, although the description has beengiven of the case, as an example, where the polarizing plate is bondedto the light emission surface of the light guide plate of the frontlight unit at the side of the liquid crystal panel surface, in additionto this case, a desired effect can be obtained also when this embodimentis applied to a case where the light guide plate is bonded to the lightguide plate at the side of the outside light incident surface, a casewhere it is bonded to the liquid crystal panel surface, or a case whereit is bonded to the light guide plate of the backlight unit.

Besides, the structure of the polarizing plate will be specificallydescribed. As the polarizing plate, there is, for example, a polarizingfilm single body in which polyvinyl alcohol (PVA) is drawn and iscolored with iodine, a polarizing plate having such a structure that forexample, triacetyl cellulose (TAC) films as protection films are bondedto both sides of the polarizing film, or a polarizing plate in whichretardation films having different linear expansion coefficients arelaminated. This embodiment can be applied to all of the above polarizingplates.

The invention is not limited to the above embodiment, but can bevariously modified.

For example, in the above embodiment, although the active matrix typeliquid crystal display device is exemplified, the invention is notlimited to this, but can also be applied to a simple matrix liquidcrystal display device.

Besides, in the above embodiment, although the description has beengiven of the case where the light-emitting area is divided into fourareas, the invention is not limited to this, and the area can be dividedinto an arbitrary number of areas.

Further, in the above embodiment, although the TN mode liquid crystaldisplay device is exemplified, the invention is not limited to this, butcan be applied to another liquid crystal display device such as an MVAmode one or an IPS mode one.

Seventh Embodiment

A liquid crystal display device according to a seventh embodiment of theinvention will be described with reference to FIGS. 77 to 85. Thisembodiment relates to the liquid crystal display device including avertical aligned liquid crystal display area.

FIG. 84 is a schematic structural view showing a main part of an exampleof a conventional liquid crystal display device (for example, see patentdocument 8). In FIG. 84, reference numeral 201 denotes an active matrixtype color liquid crystal display panel in which thin film transistors(TFTs) are used as switching elements and which operates in a verticalalignment mode; 202, a backlight as a light source of the color liquidcrystal display panel; and 203, an inverter as a power source of thebacklight 202.

Reference numeral 204 denotes a data driver (data line driving circuit)for outputting RGB signals to data lines formed in the color liquidcrystal display panel 201; and 205, a gate driver (gate line drivingcircuit) for outputting gate signals (scanning signals) to gate linesformed in the color liquid crystal display panel 201.

Reference numeral 206 denotes a timing controller which receives a dotclock DCLK given from a display signal source (for example, a computer),a vertical synchronization signal Vsync, a display signalsynchronization signal (display signal effective area specified signal)ENAB and RGB data signals R0 to R6, G0 to G6, and B0 to B6, and suppliesvarious signals necessary for driving the color liquid crystal displaypanel 201 to the data driver 204 and the gate driver 205.

FIG. 85 is a timing chart showing the operation of the conventionalliquid crystal display device shown in FIG. 84, and shows the dot clockDCLK inputted to the timing controller 206, the vertical synchronizationsignal Vsync inputted to the timing controller 206, the display signalsynchronization signal ENAB inputted to the timing controller 206, theRGB data signal inputted to the timing controller 206, and the RGB datasignal given from the timing controller 206 to the data driver 204.

In the conventional liquid crystal display device shown in FIG. 84, theRGB data signals R0 to R6, G0 to G6 and B0 to B6 given from the displaysignal source are captured in the timing controller 206 insynchronization with the display signal synchronization signal ENAB, aresubjected to timing adjustment and are supplied to the data driver 204.

In the conventional liquid crystal display device shown in FIG. 84, thevertical aligned liquid crystal display panel operating in the verticalalignment mode is provided as the color liquid crystal display panel201, and the vertical aligned liquid crystal display panel has a problemthat when a picture plane is changed, in the case where an “edge” existsin the gradation displayed on a former picture plane (for example, inthe case where the background is black and a gray object having an“edge” is displayed), and a next screen is a white display, a holdingtype afterimage is apt to occur.

The holding type afterimage occurs in such a way that in a portion wherea picture plane is changed from an intermediate gradation (for example,gray) to white, when the picture plane is changed, a state in which thealignment of a liquid crystal is disturbed is held as it is, and adifference is seen against a portion where black having a uniformalignment is changed to white.

In view of the above pint, this embodiment has an object to provide aliquid crystal display device in which even in the case where a verticalaligned liquid crystal display area is included, a holding typeafterimage is made not to occur easily, and a high quality image displaycan be carried out.

This embodiment is a liquid crystal display device including a verticalaligned liquid crystal display area, and includes a black displaycontrol part which can cause a specified area of a screen to produce ablack display at a time of driving of the liquid crystal display area.

According to this embodiment, at the time of the driving of the liquidcrystal display area, since the picture plane can be made to produce theblack display by the black display control part, the alignment of theliquid crystal can be made uniform. Accordingly, the holding typeafterimage can be made not to occur easily.

Hereinafter, examples 7-1 to 7-3 of this embodiment will be describedwith reference to FIGS. 77 to 83. Incidentally, in FIGS. 77, 80 and 82,portions corresponding to those of FIG. 84 are denoted by the samesymbols and the duplicate description will be omitted.

Example 7-1

FIG. 77 is a schematic structural view showing a main part of example7-1. The example 7-1 includes an inverter 207 and a timing controller208 which are different in structure from the inverter 203 and thetiming controller 206 included in the conventional liquid crystaldisplay device shown in FIG. 84, and the other structure is the same asthe conventional liquid crystal display device shown in FIG. 84.

The inverter 207 includes a lighting control terminal 209, and in aperiod in which the lighting control terminal 209 is made to have an Llevel, a lighting state of a backlight 202 is kept, and in a period inwhich the lighting control terminal 209 is made to have an H level, thebacklight 202 is put in a non-lighting state. A lighting control signalSA is given to the lighting control terminal 209 from the timingcontroller 208.

The timing controller 208 includes a black display control part 210,supplies RGB data signals R0 to R6, G0 to G6 and B0 to B6 outputted fromthe black display control part 210 to a data driver 204, and outputs ablack display control signal generated by the black display control part210 as the lighting control signal SA, and the other part of the timingcontroller is the same as the conventionally known structure.

FIG. 78 is a circuit diagram showing the structure of the black displaycontrol part 210. In FIG. 78, reference numeral 211 denotes a blackdisplay control signal generation circuit for generating a black displaycontrol signal SB; and 212, a frame end part detection circuit whichreceives a display signal synchronization signal ENAB (or a verticalsynchronization signal Vsync) and a dot clock DCLK, detects an end partof a frame, and outputs one frame end part detection pulse SC for oneframe.

Reference numeral 213 denotes an N-pulse counter (N is, for example, 60)for counting the frame end part detection pulse SC outputted from theframe end part detection part 212; and 214, a decoder for decoding theoutput of the N-pulse counter 213 and outputting, once every N frames, ablack display control signal SB to cause one frame period to have the Hlevel.

Reference numeral 215 denotes a three-system two-input one-outputselector for selecting the RGB data signals R0 to R6, G0 to G6 and B0 toB6, or the black display data signal and supplying it to the data driver204; SL, a select control signal input terminal; A1 to A3 and B1 to B3,selected signal input terminals; and X1 to X3, output terminals.

The black display control signal SB is given to the select controlsignal input terminal SL, the R data signals R0 to R6 are given to theselected signal input terminal A1, the G data signals G0 to G6 are givento the selected signal input terminal A2, the B data signals B0 to B6are given to the selected signal input terminal A3, and the groundpotential of 0 V is given to the selected signal input terminals B1 toB3.

In the case of the black display control signal SB=L level, the selector215 selects the RGB data signals R0 to R6, G0 to G6 and B0 to B6 givento the selected signal input terminals A1 to A3 and supplies them to thedata driver 204, and in the case of the black display control signalSC=H level, the selector supplies the ground potential of 0 V given tothe selected signal input terminals B1 to B3 as the black data signal tothe data driver 204.

FIG. 79 is a timing chart showing the operation of the example 7-1, andshows the dot clock DCLK inputted to the timing controller 208, thevertical synchronization signal Vsync inputted to the timing controller208, the display synchronization signal ENAB inputted to the timingcontroller 208, the RGB data signal inputted to the timing controller208, and the RGB data signal given from the timing controller 208 to thedata driver 204.

That is, in the example 7-1, since the black display control signalgeneration circuit 211 outputs, once every N frames (for example, 60frames), the black display control signal SB to cause one frame periodto have the H level, the selector 215 supplies the RGB data signals R0to R6, G0 to G6 and B0 to B6 to the data driver 204 in the (N−1) frameperiods of the N frame periods, and supplies the black display datasignal in one frame period of the N frame periods so that a blackpicture plane is displayed on the color liquid crystal display panel201.

Besides, the black display control signal SB outputted from the blackdisplay control signal generation circuit 211 is supplied as thelighting control signal SA to the lighting control terminal 209 of theinverter 207. Accordingly, in the case where the black picture plane isdisplayed on the color liquid crystal display panel 201 by the controlof the black display control part 210, the backlight 202 is put in thenon-lighting state.

As stated above, according to the example 7-1, since the black pictureplane is displayed on the color liquid crystal display panel 201 in theone frame period of the N frame periods, even if the vertical alignmentmode color liquid crystal display panel 201 is provided, the alignmentof the liquid crystal of the whole screen can be made uniform, and theholding type afterimage can be cancelled, so that the high quality imagedisplay can be carried out.

Besides, in the case where the black picture plane is displayed on thecolor liquid crystal display panel 201 by the control of the blackdisplay control part 210, since the backlight 202 is put in thenon-lighting state, it is possible to avoid perceptually recognizing theblack display picture plane. Incidentally, also in the case where theblack picture plane is displayed on the color liquid crystal displaypanel 201 by the control of the black display control part 210, thebacklight 202 may keep the lighting state.

Example 7-2

FIG. 80 is a schematic structural view showing a main part of example7-2. The example 7-2 includes an inverter 216 and a timing controller217 which are different in structure from the inverter 203 and thetiming controller 206 included in the conventional liquid crystaldisplay device shown in FIG. 84, and the other structure is the same asthe conventional liquid crystal display device shown in FIG. 84.

When the number of horizontal lines of a color liquid crystal displaypanel 201 is 4m (m is, for example, 192), a backlight 202 includes afirst fluorescent lamp corresponding to the first to m-th horizontallines, a second fluorescent lamp corresponding to the (m+1)-th to 2m-thhorizontal lines, a third fluorescent lamp corresponding to the (2m+1)-th to 3m-th horizontal lines, and a fourth fluorescent lampcorresponding to the (3 m+1)-th to 4m-th horizontal lines. The inverter216 includes lighting control terminals 218-1 to 218-4 corresponding tothe first to the fourth fluorescent lamps.

Then, the inverter 216 keeps the lighting state of the i-th fluorescentlamp in the period when the lighting control terminal 218-i (i=1, 2, 3,4) is made to have the L level, and the inverter brings the i-thfluorescent lamp into the non-lighting state in the period when thelighting control terminal 218-i is made to have the H level. A lightingcontrol signal SAi is given to the lighting control terminal 218-i fromthe timing controller 217.

The timing controller 217 includes a black display control part 219,supplies RGB data signals R0 to R6, G0 to G6 and B0 to B6 outputted fromthe black display control part 219 to a data driver 204, and generateslighting control signals SA1 to SA4 by the black display control part219, and the other part of the timing controller is the same as theconventionally known structure.

FIG. 81 is a circuit diagram showing the structure of the black displaycontrol circuit 219. In FIG. 81, reference numeral 220 denotes a blackdisplay control signal generation circuit which receives a displaysignal synchronization signal ENAB (or a vertical synchronization signalVsync) and a dot clock DCLK, and generates a first black display controlsignal SB, and has the same circuit structure as the black displaycontrol signal generation circuit 211 shown in FIG. 78.

Reference numeral 221 denotes a black display control signal generationcircuit for generating a second black display control signal SD; 222, ahorizontal line number detection circuit which receives a display signalsynchronization signal ENAB (or a clock GCLK for a gate driver 205),detects the number of horizontal lines, and outputs one pulse SE eachtime m horizontal lines are detected; and 223, a 4-pulse counter forcounting the pulse SE outputted from the horizontal line numberdetection circuit 222.

Reference numeral 224-1 denotes a decoder which decodes the output ofthe 4-pulse counter 223, outputs the L level in a period when the countvalue of the 4-pulse counter 223 is 2, and outputs the H level in theother period. Reference numeral 224-2 denotes a decoder which decodesthe output of the 4-pulse counter 223, outputs the L level when thecount value of the 4-pulse counter 223 is 3, and outputs the H level inthe other period.

Reference numeral 224-3 denotes a decoder which decodes the output ofthe 4-pulse counter 223, outputs the L level in a period when the countvalue of the 4-pulse counter 223 is 4, and outputs the H level in theother period. Reference numeral 224-4 denotes a decoder which decodesthe output of the 4-pulse counter 223, outputs the L level in a periodwhen the count value of the 4-pulse counter 223 is 1, and outputs the Hlevel in the other period.

Reference numerals 225-1 to 225-4 denote JK flip-flops. In the JKflip-flop 225-1, the pulse SE outputted from the horizontal line numberdetection circuit 222 is given to a J terminal, and the output of thedecoder 224-1 is given to a K terminal. In the JK flip-flop 225-2, theoutput of the decoder 224-1 is given to a J terminal, and the output ofthe decoder 224-2 is given to a K terminal.

In the JK flip-flop 225-3, the output of the decoder 224-2 is given to aJ terminal, and the output of the decoder 224-3 is given to a Kterminal. In the JK flip-flop 225-4, the output of the decoder 224-3 isgiven to a J terminal, and the output of the decoder 224-4 is given to aK terminal.

Reference numeral 226 denotes a 4-input 1-output selector; A to D,selected signal input terminals; and SL1 and SL2, select control signalinput terminals. The selector 226 selects the selected signal inputterminal A at the time of SL1=L level and SL2=L level, selects theselected signal input terminal B at the time of SL1=L level and SL2=Hlevel, selects the selected signal input terminal C at the time of SL1=Hlevel and SL2=L level, and selects the selected signal input terminal Dat the time of SL1=H level and SL2=H level.

The output of the JK flip-flop 225-1 is given to the selected signalinput terminal A, the output of the JK flip-flop 225-2 is given to theselected signal input terminal B, the output of the JK flip-flop 225-3is given to the selected signal input terminal C, and the output of theJK flip-flop 225-4 is given to the selected signal input terminal D.

Reference numeral 227 denotes a black display area selection circuit,which outputs black display area selection signals SF1 and SF2 andlighting control signals SA1 to SA4, gives the black display areaselection signals SF1 and SF2 to the select control signal inputterminals SL1 and SL2 of the selector 226, and gives the lightingcontrol signals SA1 to SA4 to the lighting control terminals 218-1 to218-4 of the inverter 216.

The black display area selection circuit 227 takes a state of SF1=Llevel and SF2=L level, a state of SF1=L level and SF2=H level, a stateof SF1=H level and SF2=L level, and a state of SF1=H level and SF2=Hlevel in sequence one by one every N frames, and as a result, theselector 226 selects and outputs the outputs of the JK flip-flops 225-1to 225-4 in sequence one by one every N frame.

Reference numeral 228 denotes an AND circuit for performing an ANDoperation of the black display control signal SB outputted from theblack display control signal generation circuit 220 and the blackdisplay control signal SD outputted from the black display controlsignal generation circuit 221; 229, a 3-system 2-input 1-outputselector; SL, a select control signal input terminal; A1 to A3 and B1 toB3, selected signal input terminals; and X1 to X3, output terminals.

The output of the AND circuit 228 is given to the select control signalinput terminal SL, the R data signals R0 to R6 are given to the selectedsignal input terminal A1, the G data signals G0 to G6 are given to theselected signal input terminal A2, the B data signals B0 to B6 are givento the selected signal input terminal A3, and the ground potential of 0V is given to the selected signal input terminals B1 to B3.

In the case where the output of the AND circuit 228 is the L level, theselector 229 selects the RGB data signals R0 to R6, G0 to G6, B0 to B6given to the selected signal input terminals A1 to A3 and supplies themto the data driver 204, and in the case where the output of the ANDcircuit 228 is the H level, the selector supplies the ground potentialof 0 V given to the selected signal input terminals B1 to B3 as theblack display data signal to the data driver 204.

In the example 7-2, the black display control signal generation circuit220 outputs, once every N frames (for example, 60 frames), the blackdisplay control signal SB to cause one frame period to have the H level,and the black display control signal generation circuit 221 selects andoutputs the outputs of the JK flip-flops 225-1 to 225-4 in sequence oneby one every N frames.

As a result, the AND circuit 228 outputs the H level in the scanningperiod of the first to the m-th horizontal lines of the (N+1)-th frame,outputs the H level in the scanning period of the (m+1)-th to the 2m-thhorizontal lines of the (2N+1)-th frame, outputs the H level in thescanning period of the (2 m+1)-th to the 3m-th horizontal lines of the(3N+1)-th frame, and outputs the H level in the scanning period of the(3 m+1)-th to the 4m-th horizontal lines of the (4N+1)-th frame, andsubsequently, this operation is repeated.

That is, the area of the first to the m-th horizontal lines, the area ofthe (m+1)-th to the 2m-th horizontal lines, the area of the (2 m+1)-thto the 3m-th horizontal lines, and the area of the (3 m+1)-th to the4m-th horizontal lines are black displayed in sequence one by one everyN frames.

Then, in this example, the black display area selection circuit 227 isconstructed to output the lighting control signals SA1 to SA4 so thatthe first fluorescent lamp is turned off when the area of the first tothe m-th horizontal lines is black displayed, the second fluorescentlamp is turned off when the area of the (m+1)-th to the 2m-th horizontallines is black displayed, the third fluorescent lamp is turned off whenthe area of the (2 m+1)-th to the 3m-th horizontal lines is blackdisplayed, and the fourth fluorescent lamp is turned off when the areaof the (3 m+1)-th to the 4m-th horizontal lines is black displayed.

As stated above, according to the example 7-2, since the black pictureplane can be displayed in the four divided screen areas in the verticaldirection in sequence one by one every N frames, even if the verticalalignment mode color liquid crystal display panel 201 is included, thealignment of the liquid crystal of the whole screen can be made uniform,and the holding type afterimage can be cancelled. Accordingly, the highquality image display can be carried out.

Besides, since the fluorescent tubes provided correspondingly to theblack-displayed picture plane areas can be turned off by the lightingcontrol signals SA1 to SA4 outputted by the black display area selectioncircuit 227, it is possible to avoid perceptually recognizing the blackdisplay picture plane. Incidentally, also in the case where the blackpicture plane is displayed on the color liquid crystal display panel 201by the control of the black display control part 219, the backlight 202may keep the lighting state.

Example 7-3

FIG. 82 is a schematic structural view showing a main part of example7-3. The example 7-3 includes a backlight 202A, an inverter 230 and atiming controller 231 which are different in structure from thebacklight 202, the inverter 203 and the timing controller 206 includedin the conventional liquid crystal display device shown in FIG. 84, andthe other structure is the same as the conventional liquid crystaldisplay device shown in FIG. 84.

When the number of vertical lines of a color liquid crystal displaypanel 201 is 4n (n is, for example, 256), the backlight 202A includes afirst fluorescent lamp corresponding to the first to the n-th verticallines, a second fluorescent lamp corresponding to the (n+1)-th to the2n-th vertical lines, a third fluorescent lamp corresponding to the(2n+1)-th to the 3n-th vertical lines, and a fourth fluorescent lampcorresponding to the (3n+1)-th to the 4n-th vertical lines. The inventor230 includes lighting control terminals 232-1 to 232-4 correspondinglyto the first to the fourth fluorescent lamps.

Then, the inventor 230 keeps the lighting state of the i-th fluorescentlamp in a period when the lighting control terminal 232-i (i=1, 2, 3, 4)is made to have the L level, and brings the ith fluorescent lamp intothe non-lighting state in a period when the lighting control terminal232-i is made to have the H level. A lighting control signal SGi isgiven to the lighting control terminal 232-i from the timing controller231.

The timing controller 231 includes a black display control part 233,supplies RGB data signals R0 to R6, G0 to G6 and B0 to B6 outputted fromthe black display control part 233 to a data driver 204, and generateslighting control signals SG1 to SG4 by the black display control part233, and the other part of the timing controller is the same as theconventionally known structure.

FIG. 83 is a circuit diagram showing the structure of the black displaycontrol part 233. In FIG. 83, reference numeral 234 denotes a blackdisplay control signal generation circuit which receives a displaysignal synchronization signal ENAB (or a vertical synchronization signalVsync) and a dot clock DCLK and generates a first black display controlsignal SB, and has the same circuit structure as the black displaycontrol signal generation circuit 211 shown in FIG. 78.

Reference numeral 235 denotes a black display control signal generationcircuit for generating a second black display control signal SH; 236, adot number detection circuit which receives a display signalsynchronization signal ENAB (or a gate clock GCLK) and a dot clock DCLK,detects the number of dots, and outputs one pulse S1 each time n dotsare detected; and 237, a 4-pulse counter for counting the pulse S1outputted from the dot number detection circuit 236.

Reference numeral 238-1 denotes a decoder which decodes the output ofthe 4-pulse counter 237, outputs the L level in a period when the countvalue of the 4-pulse counter 237 is 2, and outputs the H level in theother period. Reference numeral 238-2 denotes a decoder which decodesthe output of the 4-pulse counter 237, outputs the L level in a periodwhen the count value of the 4-pulse counter 237 is 3, and outputs the Hlevel in the other period.

Reference numeral 238-3 denotes a decoder which decodes the output ofthe 4-pulse counter 237, outputs the L level in a period when the countvalue of the 4-pulse counter 237 is 4, and outputs the H level in theother period. Reference numeral 238-4 denotes a decoder which decodesthe output of the 4-pulse counter 237, outputs the L level in a periodwhen the count value of the 4-pulse counter 237 is 1, and outputs the Hlevel in the other period.

Reference numerals 239-1 to 239-4 denote JK flip-flops. In the JKflip-flop 239-1, the pulse S1 outputted from the dot number detectioncircuit 236 is given to a J terminal, and the output of the decoder238-1 is given to a K terminal. In the JK flip-flop 239-2, the output ofthe decoder 238-1 is given to a J terminal, and the output of thedecoder 238-2 is given to a K terminal.

In the JK flip-flop 239-3, the output of the decoder 239-2 is given to aJ terminal, and the output of the decoder 238-3 is given to a Kterminal. In the JK flip-flop 239-4, the output of the decoder 238-3 isgiven to a J terminal, and the output of the decoder 238-4 is given to aK terminal.

Reference numeral 240 denotes a 4-input 1-output selector; A to D,selected signal input terminals; and SL1 and SL2, select control signalinput terminals. The selector 240 selects the selected signal inputterminal A at the time of SL1=L level and SL2=L level, selects theselected signal input terminal B at the time of SL1=L level and SL2=Hlevel, selects the selected signal input terminal C at the time of SL1=Hlevel and SL2=L level, and selects the selected signal input terminal Dat the time of SL1=H level and SL2=H level.

The output of the JK flip-flop 239-1 is given to the selected signalinput terminal A, the output of the JK flip-flop 239-2 is given to theselected signal input terminal B, the output of the JK flip-flop 239-3is given to the selected signal input terminal C, and the output of theJK flip-flop 239-4 is given to the selected signal input terminal D.

Reference numeral 241 denotes a black display area selection circuit,outputs black display area selection signals SJ1 and SJ2 and lightingcontrol signals SG1 to SG4, supplies the black display area selectionsignals SJ1 and SJ2 to the select control signal input terminals SL1 andSL2 of the selector 240, and supplies the lighting control signals SG1to SG4 to the lighting control terminals 232-1 to 232-4 of the inverter230.

The black display area selection circuit 241 takes a state of SJ1=Llevel and SJ2=L level, a state of SJ1=L level and SJ2=H level, a stateof SJ1=H level and SJ2=L level, and a state of SJ1=H level and SJ2=Hlevel in sequence one by one every horizontal scanning, and as a result,the selector 240 selects and outputs the outputs of the JK flip-flop239-1 to 239-4 in sequence one by one every horizontal scanning.

Reference numeral 242 denotes an AND circuit for performing an ANDoperation of the black display control signal SB outputted from theblack display control signal generation circuit 234 and the blackdisplay control signal SH outputted from the black display controlsignal generation circuit 235; 243, a 3-system 2-input 1-outputselector; SL, a select control signal input terminal; A1 to A3 and B1 toB3, selected signal input terminals; and X1 to X3, output terminals.

The output of the AND circuit 242 is given to the select control signalinput terminal SL, the R data signals R0 to R6 are given to the selectedsignal input terminal A1, the G data signals G0 to G6 are given to theselected signal input terminal A2, the B data signals B0 to B6 are givento the selected signal input terminal A3, and the ground potential of 0V is given to the selected signal input terminals B1 to B3.

The selector 243 selects and outputs the RGB data signals R0 to R6, G0to G6 and B0 to B6, which are given to the selected signal inputterminals A1 to A3, to the data driver 204 in the case where the outputof the AND circuit 242 is the L level, and supplies the ground potentialof 0 V, which is given to the selected signal input terminals B1 to B3,as the black display data signal to the data driver 204 in the casewhere the output of the AND circuit 242 is the H level.

In the example 7-3, the black display control signal generation circuit234 outputs, once every N frames (for example, 60 frames), the blackdisplay control signal SB to cause one frame period to have the H level,and the black display control signal generation circuit 235 selects andoutputs the outputs of the JK flip-flops 239-1 to 239-4 in sequence oneby one every horizontal scanning.

As a result, the AND circuit 242 outputs the H level in the scanningperiod of the first to the n-th vertical lines of the (N+1)-th frame,outputs the H level in the scanning period of the (n+1)-th to the 2n-thvertical lines of the (2N+1) frame, outputs the H level in the scanningperiod of the (2n+1)-th to the 3n-th vertical lines of the (3N+1)-thframe, and outputs the H level in the scanning period of the (3n+1)-thto the 4n-th vertical lines of the (4N+1)-th frame, and subsequently,this operation is repeated.

That is, the area of the first to the n-th vertical lines, the area ofthe (n+1)-th to the 2n-th vertical lines, the area of the (2n+1)-th tothe 3n-th vertical lines, and the area of the (3n+1)-th to the 4n-thvertical lines are black displayed in sequence one by one every Nframes.

Then, in this example, the black display area selection circuit 241 isconstructed to output the lighting control signals SG1 to SG4 so thatthe first fluorescent lamp is turned off when the area of the first tothe n-th vertical lines is black displayed, the second fluorescent lampis turned off when the area of the (n+1)-th to the 2n-th vertical linesis black displayed, the third fluorescent lamp is turned off when thearea of the (2n+1)-th to the 3n-th vertical lines is black displayed,and the fourth fluorescent lamp is turned off when the area of the(3n+1)-th to the 4n-th vertical lines are black displayed.

As stated above, according to the example 7-3, since the black pictureplane can be displayed in the four divided screen areas in thehorizontal direction in sequence one by one every N frames, even if thevertical alignment mode color liquid crystal display panel 201 isincluded, the alignment of the liquid crystal of the whole screen can bemade uniform, and the holding type afterimage can be cancelled.Accordingly, the high quality image display can be carried out.

Besides, since the fluorescent tubes provided correspondingly to theblack-displayed screen areas can be turned off by the lighting controlsignals SG1 to SG4 outputted by the black display area selection circuit241, it is possible to avoid perceptually recognizing the black displaypicture plane. Incidentally, also in the case where the black pictureplane is displayed on the color liquid crystal display panel 201 by thecontrol of the black display control part 233, the backlight 202A maykeep the lighting state.

Incidentally, in the example 7-1 to the example 7-3, although the wholearea or partial area of the screen is black displayed in one frameperiod every N frames, instead of this, the whole area or partial areaof the screen may be black displayed in several continuous frame periodsevery N frames.

As described above, according to this embodiment, since the screen canbe black displayed by the black display control part at the time of thedriving of the liquid crystal display area, the alignment of the liquidcrystal can be made uniform, and even in the case where the verticalaligned liquid crystal display area is included, the holding typeafterimage is made not to easily occur, and the high quality imagedisplay can be carried out.

As described above, according to the invention, it is possible torealize the illumination device in which while the drop of the displaybrightness is suppressed, the movement blurring and the tailingphenomenon in the motion picture display can be reduced, and the liquidcrystal display device using the same.

Besides, according to the invention, it is possible to realize theillumination device which can suppress consumed electric power and inwhich the device can be made to be small and light and to have longlifetime, and the liquid crystal display device using the same.

1. A liquid crystal display device, comprising: an LCD panel modulatinglight transmissivities of plural pixels disposed in a matrix form on thebasis of respective gradation data; an illumination device forirradiating light to the respective pixels while a ratio (duty ratio) ofa lighting time in one frame period is changed; and a display dataconversion part for calculating respective lightnesses and a lightnesshistogram from the respective gradation data, determining a thresholdlightness from the lightness histogram on the basis of a previouslydetermined ratio of pixels to be saturated in brightness, processing therespective gradation data on the basis of the threshold lightness tooutput them to the LCD panel, and outputting duty ratio data to changethe duty ratio to the illumination device.
 2. A liquid crystal displaydevice according to claim 1, wherein the display data conversion partcounts the lightnesses from the lightness histogram in descending orderof lightness on the basis of the ratio of the pixels to be saturated inbrightness and determines the threshold lightness.
 3. A liquid crystaldisplay device according to claim 2, wherein the display data conversionpart judges M (M≦N) pixels, in which an image is displayed, of N pixelsin one frame, and determines the threshold lightness on the basis of aproduct of the number of the M pixels and the ratio of the pixels to besaturated in brightness.
 4. A liquid crystal display device according toclaim 1, wherein the display data conversion part determines the dutyratio so that a product of a maximum value which the gradation data cantake and the duty ratio becomes equal to the threshold lightness,processes the gradation data of a pixel of a lightness not lower thanthe threshold lightness to have the maximum value, and processes thegradation data of the other pixel so that a product of the processedgradation data and the determined duty ratio becomes equal to lightnessof the original gradation data of the pixel.
 5. A liquid crystal displaydevice according to claim 1, wherein the lightness is obtained from thegradation data (R, G, B) of the respective pixels as the lightnessY=r×R+g×G+b×B (r, g and b are real numbers and includes a numericalvalue of 0).